Qpdf Manual

User Manual:

Open the PDF directly: View PDF PDF.
Page Count: 64

Open PDF In BrowserView PDF
QPDF Manual
For QPDF Version 8.3.0, January 7, 2019
Jay Berkenbilt

QPDF Manual: For QPDF Version 8.3.0, January 7, 2019
Jay Berkenbilt
Copyright © 2005–2019 Jay Berkenbilt

Table of Contents
General Information ............................................................................................................................ v
1. What is QPDF? .............................................................................................................................. 1
2. Building and Installing QPDF ........................................................................................................... 2
2.1. System Requirements ............................................................................................................ 2
2.2. Build Instructions ................................................................................................................. 2
2.3. Notes for Packagers .............................................................................................................. 3
3. Running QPDF ............................................................................................................................... 4
3.1. Basic Invocation ................................................................................................................... 4
3.2. Shell Completion .................................................................................................................. 4
3.3. Basic Options ...................................................................................................................... 4
3.4. Encryption Options ............................................................................................................... 7
3.5. Page Selection Options .......................................................................................................... 9
3.6. Advanced Parsing Options .................................................................................................... 11
3.7. Advanced Transformation Options ......................................................................................... 11
3.8. Testing, Inspection, and Debugging Options ............................................................................ 16
4. QDF Mode ................................................................................................................................... 19
5. Using the QPDF Library ................................................................................................................ 21
5.1. Using QPDF from C++ ........................................................................................................ 21
5.2. Using QPDF from other languages ......................................................................................... 21
6. QPDF JSON ................................................................................................................................. 22
6.1. Overview ........................................................................................................................... 22
6.2. JSON Guarantees ................................................................................................................ 22
6.3. Limitations of JSON Representation ....................................................................................... 23
6.4. JSON: Special Considerations ............................................................................................... 23
7. Design and Library Notes ............................................................................................................... 25
7.1. Introduction ....................................................................................................................... 25
7.2. Design Goals ...................................................................................................................... 25
7.3. Helper Classes .................................................................................................................... 26
7.4. Implementation Notes .......................................................................................................... 27
7.5. Casting Policy .................................................................................................................... 28
7.6. Encryption ......................................................................................................................... 30
7.7. Random Number Generation ................................................................................................. 30
7.8. Adding and Removing Pages ................................................................................................ 30
7.9. Reserving Object Numbers ................................................................................................... 31
7.10. Copying Objects From Other PDF Files ................................................................................ 31
7.11. Writing PDF Files ............................................................................................................. 31
7.12. Filtered Streams ................................................................................................................ 32
8. Linearization ................................................................................................................................. 34
8.1. Basic Strategy for Linearization ............................................................................................. 34
8.2. Preparing For Linearization .................................................................................................. 34
8.3. Optimization ...................................................................................................................... 34
8.4. Writing Linearized Files ....................................................................................................... 35
8.5. Calculating Linearization Data .............................................................................................. 35
8.6. Known Issues with Linearization ........................................................................................... 35
8.7. Debugging Note .................................................................................................................. 36
9. Object and Cross-Reference Streams ................................................................................................. 37
9.1. Object Streams ................................................................................................................... 37
9.2. Cross-Reference Streams ...................................................................................................... 37
9.2.1. Cross-Reference Stream Data ..................................................................................... 38
9.3. Implications for Linearized Files ........................................................................................... 38
9.4. Implementation Notes .......................................................................................................... 39


QPDF Manual

A. Release Notes ..............................................................................................................................
B. Upgrading from 2.0 to 2.1 ..............................................................................................................
C. Upgrading to 3.0 ...........................................................................................................................
D. Upgrading to 4.0 ..........................................................................................................................



General Information
QPDF is a program that does structural, content-preserving transformations on PDF files. QPDF's website is located
at http://qpdf.sourceforge.net/. QPDF's source code is hosted on github at https://github.com/qpdf/qpdf.
QPDF is licensed under the Apache License, Version 2.0 [http://www.apache.org/licenses/LICENSE-2.0] (the "License"). Unless required by applicable law or agreed to in writing, software distributed under the License is distributed
See the License for the specific language governing permissions and limitations under the License.
Versions of qpdf prior to version 7 were released under the terms of the Artistic License, version 2.0 [https://opensource.org/licenses/Artistic-2.0]. At your option, you may continue to consider qpdf to be licensed under those terms.
The Apache License 2.0 permits everything that the Artistic License 2.0 permits but is slightly less restrictive. Allowing the Artistic License to continue being used is primary to help people who may have to get specific approval to
use qpdf in their products.
QPDF is intentionally released with a permissive license. However, if there is some reason that the licensing terms
don't work for your requirements, please feel free to contact the copyright holder to make other arrangements.
QPDF was originally created in 2001 and modified periodically between 2001 and 2005 during my employment at
Apex CoVantage [http://www.apexcovantage.com]. Upon my departure from Apex, the company graciously allowed
me to take ownership of the software and continue maintaining as an open source project, a decision for which I am
very grateful. I have made considerable enhancements to it since that time. I feel fortunate to have worked for people
who would make such a decision. This work would not have been possible without their support.


Chapter 1. What is QPDF?
QPDF is a program that does structural, content-preserving transformations on PDF files. It could have been called
something like pdf-to-pdf. It also provides many useful capabilities to developers of PDF-producing software or for
people who just want to look at the innards of a PDF file to learn more about how they work.
With QPDF, it is possible to copy objects from one PDF file into another and to manipulate the list of pages in a PDF
file. This makes it possible to merge and split PDF files. The QPDF library also makes it possible for you to create
PDF files from scratch. In this mode, you are responsible for supplying all the contents of the file, while the QPDF
library takes care off all the syntactical representation of the objects, creation of cross references tables and, if you
use them, object streams, encryption, linearization, and other syntactic details. You are still responsible for generating
PDF content on your own.
QPDF has been designed with very few external dependencies, and it is intentionally very lightweight. QPDF is not a
PDF content creation library, a PDF viewer, or a program capable of converting PDF into other formats. In particular,
QPDF knows nothing about the semantics of PDF content streams. If you are looking for something that can do that,
you should look elsewhere. However, once you have a valid PDF file, QPDF can be used to transform that file in ways
perhaps your original PDF creation can't handle. For example, many programs generate simple PDF files but can't
password-protect them, web-optimize them, or perform other transformations of that type.


Chapter 2. Building and Installing
This chapter describes how to build and install qpdf. Please see also the README.md and INSTALL files in the source

2.1. System Requirements
The qpdf package has few external dependencies. In order to build qpdf, the following packages are required:
• zlib: http://www.zlib.net/
• jpeg: http://www.ijg.org/files/ or https://libjpeg-turbo.org/
• gnu make 3.81 or newer: http://www.gnu.org/software/make
• perl version 5.8 or newer: http://www.perl.org/; required for fix-qdf and the test suite.
• GNU diffutils (any version): http://www.gnu.org/software/diffutils/ is required to run the test suite. Note that this is
the version of diff present on virtually all GNU/Linux systems. This is required because the test suite uses diff -u.
• A C++ compiler that works well with STL and has the long long type. Most modern C++ compilers should fit
the bill fine. QPDF is tested with gcc, clang, and Microsoft Visual C++.
Part of qpdf's test suite does comparisons of the contents PDF files by converting them images and comparing the
images. The image comparison tests are disabled by default. Those tests are not required for determining correctness of
a qpdf build if you have not modified the code since the test suite also contains expected output files that are compared
literally. The image comparison tests provide an extra check to make sure that any content transformations don't break
the rendering of pages. Transformations that affect the content streams themselves are off by default and are only
provided to help developers look into the contents of PDF files. If you are making deep changes to the library that cause
changes in the contents of the files that qpdf generates, then you should enable the image comparison tests. Enable
them by running configure with the --enable-test-compare-images flag. If you enable this, the following additional
requirements are required by the test suite. Note that in no case are these items required to use qpdf.
• libtiff: http://www.remotesensing.org/libtiff/
• GhostScript version 8.60 or newer: http://www.ghostscript.com
If you do not enable this, then you do not need to have tiff and ghostscript.
If Adobe Reader is installed as acroread, some additional test cases will be enabled. These test cases simply verify
that Adobe Reader can open the files that qpdf creates. They require version 8.0 or newer to pass. However, in order
to avoid having qpdf depend on non-free (as in liberty) software, the test suite will still pass without Adobe reader,
and the test suite still exercises the full functionality of the software.
Pre-built documentation is distributed with qpdf, so you should generally not need to rebuild the documentation. In
order to build the documentation from its docbook sources, you need the docbook XML style sheets (http://downloads.sourceforge.net/docbook/). To build the PDF version of the documentation, you need Apache fop (http://xml.apache.org/fop/) version 0.94 or higher.

2.2. Build Instructions
Building qpdf on UNIX is generally just a matter of running


Building and Installing QPDF

You can also run make check to run the test suite and make install to install. Please run ./configure --help for options
on what can be configured. You can also set the value of DESTDIR during installation to install to a temporary location,
as is common with many open source packages. Please see also the README.md and INSTALL files in the source
Building on Windows is a little bit more complicated. For details, please see README-windows.md in the source
distribution. You can also download a binary distribution for Windows. There is a port of qpdf to Visual C++ version 6
in the contrib area generously contributed by Jian Ma. This is also discussed in more detail in README-windows.md.
There are some other things you can do with the build. Although qpdf uses autoconf, it does not use automake but
instead uses a hand-crafted non-recursive Makefile that requires gnu make. If you're really interested, please read the
comments in the top-level Makefile.

2.3. Notes for Packagers
If you are packaging qpdf for an operating system distribution, here are some things you may want to keep in mind:
• Passing --enable-show-failed-test-output to ./configure will cause any failed test output to be written to the console. This can be very useful for seeing test failures generated by autobuilders where you can't access qtest.log after
the fact.
• If qpdf's build environment detects the presence of autoconf and related tools, it will check to ensure that automatically generated files are up-to-date with recorded checksums and fail if it detects a discrepancy. This feature is
intended to prevent you from accidentally forgetting to regenerate automatic files after modifying their sources. If
your packaging environment automatically refreshes automatic files, it can cause this check to fail. Supress qpdf's
checks by passing --disable-check-autofiles to /.configure. This is safe since qpdf's autogen.sh just runs autotools
in the normal way.
• QPDF's make install does not install completion files by default, but as a packager, it's good if you install them
wherever your distribution expects such files to go. You can find completion files to install in the completions
• Packagers are encouraged to install the source files from the examples directory along with qpdf development packages.


Chapter 3. Running QPDF
This chapter describes how to run the qpdf program from the command line.

3.1. Basic Invocation
When running qpdf, the basic invocation is as follows:
qpdf [ options ] infilename [ outfilename ]
This converts PDF file infilename to PDF file outfilename. The output file is functionally identical to the input file but
may have been structurally reorganized. Also, orphaned objects will be removed from the file. Many transformations
are available as controlled by the options below. In place of infilename, the parameter --empty may be specified. This
causes qpdf to use a dummy input file that contains zero pages. The only normal use case for using --empty would be if
you were going to add pages from another source, as discussed in Section 3.5, “Page Selection Options”, page 9.
If @filename appears anywhere in the command-line, it will be read line by line, and each line will be treated as
a command-line argument. The @- option allows arguments to be read from standard input. This allows qpdf to be
invoked with an arbitrary number of arbitrarily long arguments. It is also very useful for avoiding having to pass
passwords on the command line.
outfilename does not have to be seekable, even when generating linearized files. Specifying “-” as outfilename means
to write to standard output. However, you can't specify the same file as both the input and the output because qpdf reads
data from the input file as it writes to the output file. QPDF attempts to detect this case and fail without overwriting
the output file.
Most options require an output file, but some testing or inspection commands do not. These are specifically noted.

3.2. Shell Completion
Starting in qpdf version 8.3.0, qpdf provides its own completion support for zsh and bash. You can enable bash completion with eval $(qpdf --completion-bash) and zsh completion with eval $(qpdf --completion-zsh). If qpdf is not
in your path, you should invoke it above with an absolute path. If you invoke it with a relative path, it will warn you,
and the completion won't work if you're in a different directory.

3.3. Basic Options
The following options are the most common ones and perform commonly needed transformations.
Display command-line invocation help.
Display the current version of qpdf.
Show detailed copyright information.


Running QPDF

Output a completion command you can eval to enable shell completion from bash.
Output a completion command you can eval to enable shell completion from zsh.
Specifies a password for accessing encrypted files. Note that you can use @filename or @- as described above
to put the password in a file or pass it via standard input so you can avoid specifying it on the command line.
Increase verbosity of output. For now, this just prints some indication of any file that it creates.
Indicate progress while writing files.
Suppress writing of warnings to stderr. If warnings were detected and suppressed, qpdf will still exit with exit
code 3.
Causes generation of a linearized (web-optimized) output file.
Encrypt the file using the same encryption parameters, including user and owner password, as the specified file.
Use --encrypt-file-password to specify a password if one is needed to open this file. Note that copying the
encryption parameters from a file also copies the first half of /ID from the file since this is part of the encryption
If the file specified with --copy-encryption requires a password, specify the password using this option. Note
that only one of the user or owner password is required. Both passwords will be preserved since QPDF does
not distinguish between the two passwords. It is possible to preserve encryption parameters, including the owner
password, from a file even if you don't know the file's owner password.
--encrypt options -Causes generation an encrypted output file. Please see Section 3.4, “Encryption Options”, page 7 for details
on how to specify encryption parameters.
Removes any encryption on the file. A password must be supplied if the file is password protected.
Overrides the usual computation/retrieval of the PDF file's encryption key from user/owner password with an
explicit specification of the encryption key. When this option is specified, the argument to the --password option


Running QPDF

is interpreted as a hexadecimal-encoded key value. This only applies to the password used to open the main input
file. It does not apply to other files opened by --pages or other options or to files being written.
Most users will never have a need for this option, and no standard viewers support this mode of operation, but
it can be useful for forensic or investigatory purposes. For example, if a PDF file is encrypted with an unknown
password, a brute-force attack using the key directly is sometimes more efficient than one using the password.
Also, if a file is heavily damaged, it may be possible to derive the encryption key and recover parts of the file
using it directly. To expose the encryption key used by an encrypted file that you can open normally, use the -show-encryption-key option.
Apply rotation to specified pages. The page-range portion of the option value has the same format as page ranges
in Section 3.5, “Page Selection Options”, page 9. If the page range is omitted, the rotation is applied to all
pages. The angle portion of the parameter may be either 90, 180, or 270. If preceded by + or -, the angle is added
to or subtracted from the specified pages' original rotations. Otherwise the pages' rotations are set to the exact
value. For example, the command qpdf in.pdf out.pdf --rotate=+90:2,4,6 --rotate=180:7-8 would rotate pages
2, 4, and 6 90 degrees clockwise from their original rotation and force the rotation of pages 7 through 9 to 180
degrees regardless of their original rotation, and the command qpdf in.pdf out.pdf --rotate=180 would rotate
all pages by 180 degrees.
This option controls whether qpdf keeps individual files open while merging. Prior to version 8.1.0, qpdf always
kept all files open, but this meant that the number of files that could be merged was limited by the operating
system's open file limit. Version 8.1.0 opened files as they were referenced and closed them after each read, but
this caused a major performance impact. Version 8.2.0 optimized the performance but did so in a way that, for local
file systems, there was a small but unavoidable performance hit, but for networked file systems, the performance
impact could be very high. Starting with version 8.2.1, the default behavior is that files are kept open if no more
than 200 files are specified, but that the behavior can be explicitly overridden with the --keep-files-open flag. If
you are merging more than 200 files but less than the operating system's max open files limit, you may want to use
--keep-files-open=y, especially if working over a networked file system. If you are using a local file system where
the overhead is low and you might sometimes merge more than the OS limit's number of files from a script and
are not worried about a few seconds additional processing time, you may want to specify --keep-files-open=n.
--pages options -Select specific pages from one or more input files. See Section 3.5, “Page Selection Options”, page 9 for
details on how to do page selection (splitting and merging).
When specified, collate rather than concatenate pages from files specified with --pages. See Section 3.5, “Page
Selection Options”, page 9 for additional details.
Write each group of n pages to a separate output file. If n is not specified, create single pages. Output file names
are generated as follows:
• If the string %d appears in the output file name, it is replaced with a range of zero-padded page numbers starting
from 1.
• Otherwise, if the output file name ends in .pdf (case insensitive), a zero-padded page range, preceded by a dash,
is inserted before the file extension.


Running QPDF

• Otherwise, the file name is appended with a zero-padded page range preceded by a dash.
Page ranges are a single number in the case of single-page groups or two numbers separated by a dash otherwise.
For example, if infile.pdf has 12 pages
• qpdf --split-pages infile.pdf %d-out would generate files 01-out through 12-out
• qpdf --split-pages=2 infile.pdf outfile.pdf would generate files outfile-01-02.pdf through outfile-11-12.pdf
• qpdf --split-pages infile.pdf something.else would generate files something.else-01 through something.else-12
Note that outlines, threads, and other global features of the original PDF file are not preserved. For each page
of output, this option creates an empty PDF and copies a single page from the output into it. If you require the
global data, you will have to run qpdf with the --pages option once for each file. Using --split-pages is much
faster if you don't require the global data.
Password-protected files may be opened by specifying a password. By default, qpdf will preserve any encryption data
associated with a file. If --decrypt is specified, qpdf will attempt to remove any encryption information. If --encrypt
is specified, qpdf will replace the document's encryption parameters with whatever is specified.
Note that qpdf does not obey encryption restrictions already imposed on the file. Doing so would be meaningless since
qpdf can be used to remove encryption from the file entirely. This functionality is not intended to be used for bypassing
copyright restrictions or other restrictions placed on files by their producers.
In all cases where qpdf allows specification of a password, care must be taken if the password contains characters
that fall outside of the 7-bit US-ASCII character range to ensure that the exact correct byte sequence is provided. It
is possible that a future version of qpdf may handle this more gracefully. For example, if a password was encrypted
using a password that was encoded in ISO-8859-1 and your terminal is configured to use UTF-8, the password you
supply may not work properly. There are various approaches to handling this. For example, if you are using Linux
and have the iconv executable installed, you could pass --password=`echo password | iconv -t iso-8859-1` to qpdf
where password is a password specified in your terminal's locale. A detailed discussion of this is out of scope for
this manual, but just be aware of this issue if you have trouble with a password that contains 8-bit characters.

3.4. Encryption Options
To change the encryption parameters of a file, use the --encrypt flag. The syntax is
--encrypt user-password owner-password key-length [ restrictions ] -Note that “--” terminates parsing of encryption flags and must be present even if no restrictions are present.
Either or both of the user password and the owner password may be empty strings.
The value for key-length may be 40, 128, or 256. The restriction flags are dependent upon key length. When no
additional restrictions are given, the default is to be fully permissive.
If key-length is 40, the following restriction options are available:
Determines whether or not to allow printing.
Determines whether or not to allow document modification.


Running QPDF

Determines whether or not to allow text/image extraction.
Determines whether or not to allow comments and form fill-in and signing.
If key-length is 128, the following restriction options are available:
Determines whether or not to allow accessibility to visually impaired.
Determines whether or not to allow text/graphic extraction.
Controls printing access. print-opt may be one of the following:
• full: allow full printing
• low: allow low-resolution printing only
• none: disallow printing
Controls modify access. modify-opt may be one of the following, each of which implies all the options that
follow it:
• all: allow full document modification
• annotate: allow comment authoring and form operations
• form: allow form field fill-in and signing
• assembly: allow document assembly only
• none: allow no modifications
If specified, any metadata stream in the document will be left unencrypted even if the rest of the document is
encrypted. This also forces the PDF version to be at least 1.5.
If --use-aes=y is specified, AES encryption will be used instead of RC4 encryption. This forces the PDF version
to be at least 1.6.
Use of this option forces the /V and /R parameters in the document's encryption dictionary to be set to the value
4. As qpdf will automatically do this when required, there is no reason to ever use this option. It exists primarily
for use in testing qpdf itself. This option also forces the PDF version to be at least 1.5.


Running QPDF

If key-length is 256, the minimum PDF version is 1.7 with extension level 8, and the AES-based encryption format
used is the PDF 2.0 encryption method supported by Acrobat X. the same options are available as with 128 bits with
the following exceptions:
This option is not available with 256-bit keys. AES is always used with 256-bit encryption keys.
This option is not available with 256 keys.
If specified, qpdf sets the minimum version to 1.7 at extension level 3 and writes the deprecated encryption format
used by Acrobat version IX. This option should not be used in practice to generate PDF files that will be in general
use, but it can be useful to generate files if you are trying to test proper support in another application for PDF
files encrypted in this way.
The default for each permission option is to be fully permissive.

3.5. Page Selection Options
Starting with qpdf 3.0, it is possible to split and merge PDF files by selecting pages from one or more input files.
Whatever file is given as the primary input file is used as the starting point, but its pages are replaced with pages as
--pages input-file [ --password=password ] [ page-range ] [ ... ] -Multiple input files may be specified. Each one is given as the name of the input file, an optional password (if required
to open the file), and the range of pages. Note that “--” terminates parsing of page selection flags.
For each file that pages should be taken from, specify the file, a password needed to open the file (if any), and a page
range. The password needs to be given only once per file. If any of the input files are the same as the primary input
file or the file used to copy encryption parameters (if specified), you do not need to repeat the password here. The
same file can be repeated multiple times. If a file that is repeated has a password, the password only has to be given
the first time. All non-page data (info, outlines, page numbers, etc.) are taken from the primary input file. To discard
these, use --empty as the primary input.
Starting with qpdf 5.0.0, it is possible to omit the page range. If qpdf sees a value in the place where it expects a page
range and that value is not a valid range but is a valid file name, qpdf will implicitly use the range 1-z, meaning that
it will include all pages in the file. This makes it possible to easily combine all pages in a set of files with a command
like qpdf --empty out.pdf --pages *.pdf --.
It is not presently possible to specify the same page from the same file directly more than once, but you can make this
work by specifying two different paths to the same file (such as by putting ./ somewhere in the path). This can also be
used if you want to repeat a page from one of the input files in the output file. This may be made more convenient in
a future version of qpdf if there is enough demand for this feature.
The page range is a set of numbers separated by commas, ranges of numbers separated dashes, or combinations of
those. The character “z” represents the last page. A number preceded by an “r” indicates to count from the end, so
r3-r1 would be the last three pages of the document. Pages can appear in any order. Ranges can appear with a high
number followed by a low number, which causes the pages to appear in reverse. Repeating a number will cause an
error, but you can use the workaround discussed above should you really want to include the same page twice.


Running QPDF

Example page ranges:
• 1,3,5-9,15-12: pages 1, 3, 5, 6, 7, 8, 9, 15, 14, 13, and 12 in that order.
• z-1: all pages in the document in reverse
• r3-r1: the last three pages of the document
• r1-r3: the last three pages of the document in reverse order
Starting in qpdf version 8.3, you can specify the --collate option. Note that this option is specified outside of -pages ... --. When --collate is specified, it changes the meaning of --pages so that the specified files, as modified by
page ranges, are collated rather than concatenated. For example, if you add the files odd.pdf and even.pdf containing
odd and even pages of a document respectively, you could run qpdf --collate odd.pdf --pages odd.pdf even.pdf -all.pdf to collate the pages. This would pick page 1 from odd, page 1 from even, page 2 from odd, page 2 from even,
etc. until all pages have been included. Any number of files and page ranges can be specified. If any file has fewer
pages, that file is just skipped when its pages have all been included. For example, if you ran qpdf --collate --empty
--pages a.pdf 1-5 b.pdf 6-4 c.pdf r1 -- out.pdf, you would get the following pages in this order:
• a.pdf page 1
• b.pdf page 6
• c.pdf last page
• a.pdf page 2
• b.pdf page 5
• a.pdf page 3
• b.pdf page 4
• a.pdf page 4
• a.pdf page 5
Starting in qpdf version 8.3, when you split and merge files, any page labels (page numbers) are preserved in the
final file. It is expected that more document features will be preserved by splitting and merging. In the mean time,
semantics of splitting and merging vary across features. For example, the document's outlines (bookmarks) point to
actual page objects, so if you select some pages and not others, bookmarks that point to pages that are in the output
file will work, and remaining bookmarks will not work. A future version of qpdf may do a better job at handling these
issues. (Note that the qpdf library already contains all of the APIs required in order to implement this in your own
application if you need it.) In the mean time, you can always use --empty as the primary input file to avoid copying
all of that from the first file. For example, to take pages 1 through 5 from a infile.pdf while preserving all metadata
associated with that file, you could use
qpdf infile.pdf --pages infile.pdf 1-5 -- outfile.pdf
If you wanted pages 1 through 5 from infile.pdf but you wanted the rest of the metadata to be dropped, you could
instead run
qpdf --empty --pages infile.pdf 1-5 -- outfile.pdf
If you wanted to take pages 1–5 from file1.pdf and pages 11–15 from file2.pdf in reverse, you would run


Running QPDF

qpdf file1.pdf --pages file1.pdf 1-5 file2.pdf 15-11 -- outfile.pdf
If, for some reason, you wanted to take the first page of an encrypted file called encrypted.pdf with password pass
and repeat it twice in an output file, and if you wanted to drop document-level metadata but preserve encryption, you
would use
qpdf --empty --copy-encryption=encrypted.pdf --encryption-file-password=pass
--pages encrypted.pdf --password=pass 1 ./encrypted.pdf --password=pass 1 -outfile.pdf
Note that we had to specify the password all three times because giving a password as --encryption-file-password
doesn't count for page selection, and as far as qpdf is concerned, encrypted.pdf and ./encrypted.pdf are separated files.
These are all corner cases that most users should hopefully never have to be bothered with.

3.6. Advanced Parsing Options
These options control aspects of how qpdf reads PDF files. Mostly these are of use to people who are working with
damaged files. There is little reason to use these options unless you are trying to solve specific problems. The following
options are available:
Prevents qpdf from attempting to recover damaged files.
Tells qpdf to ignore any cross-reference streams.
Ordinarily, qpdf will attempt to recover from certain types of errors in PDF files. These include errors in the crossreference table, certain types of object numbering errors, and certain types of stream length errors. Sometimes, qpdf
may think it has recovered but may not have actually recovered, so care should be taken when using this option as
some data loss is possible. The --suppress-recovery option will prevent qpdf from attempting recovery. In this case,
it will fail on the first error that it encounters.
Ordinarily, qpdf reads cross-reference streams when they are present in a PDF file. If --ignore-xref-streams is specified, qpdf will ignore any cross-reference streams for hybrid PDF files. The purpose of hybrid files is to make some
content available to viewers that are not aware of cross-reference streams. It is almost never desirable to ignore them.
The only time when you might want to use this feature is if you are testing creation of hybrid PDF files and wish to
see how a PDF consumer that doesn't understand object and cross-reference streams would interpret such a file.

3.7. Advanced Transformation Options
These transformation options control fine points of how qpdf creates the output file. Mostly these are of use only to
people who are very familiar with the PDF file format or who are PDF developers. The following options are available:
By default, or with --compress-streams=y, qpdf will compress any stream with no other filters applied to it with
the /FlateDecode filter when it writes it. To suppress this behavior and preserve uncompressed streams as
uncompressed, use --compress-streams=n.
Controls which streams qpdf tries to decode. The default is generalized. The following options are available:


Running QPDF

• none: do not attempt to decode any streams
• generalized: decode streams filtered with supported generalized filters: /LZWDecode, /FlateDecode, /
ASCII85Decode, and /ASCIIHexDecode. We define generalized filters as those to be used for general-purpose compression or encoding, as opposed to filters specifically designed for image data.
• specialized: in addition to generalized, decode streams with supported non-lossy specialized filters; currently
this is just /RunLengthDecode
• all: in addition to generalized and specialized, decode streams with supported lossy filters; currently this is just
/DCTDecode (JPEG)
Controls transformation of stream data. This option predates the --compress-streams and --decode-level options.
Those options can be used to achieve the same affect with more control. The value of option may be one of
the following:
• compress: recompress stream data when possible (default); equivalent to --compress-streams=y --decode-level=generalized
• preserve: leave all stream data as is; equivalent to --compress-streams=n --decode-level=none
• uncompress: uncompress stream data compressed with generalized filters when possible; equivalent to --compress-streams=n --decode-level=generalized
Enables or disables normalization of content streams. Content normalization is enabled by default in QDF mode.
Please see Chapter 4, QDF Mode, page 19 for additional discussion of QDF mode.
Controls handling of object streams. The value of mode may be one of the following:
• preserve: preserve original object streams (default)
• disable: don't write any object streams
• generate: use object streams wherever possible
Tells qpdf to preserve objects that are not referenced when writing the file. Ordinarily any object that is not
referenced in a traversal of the document from the trailer dictionary will be discarded. This may be useful in
working with some damaged files or inspecting files with known unreferenced objects.
This flag is ignored for linearized files and has the effect of causing objects in the new file to be written in order
by object ID from the original file. This does not mean that object numbers will be the same since qpdf may
create stream lengths as direct or indirect differently from the original file, and the original file may have gaps
in its numbering.
See also --preserve-unreferenced-resources, which does something completely different.
Starting with qpdf 8.1, when splitting pages, qpdf ordinarily attempts to remove images and fonts that are not used
by a page even if they are referenced in the page's resources dictionary. This option suppresses that behavior. The


Running QPDF

only reason to use this is if you suspect that qpdf is removing resources it shouldn't be removing. If you encounter
that case, please report it as a bug.
See also --preserve-unreferenced-resources, which does something completely different.
Tells qpdf to insert a newline before the endstream keyword, not counted in the length, after any stream content
even if the last character of the stream was a newline. This may result in two newlines in some cases. This is
a requirement of PDF/A. While qpdf doesn't specifically know how to generate PDF/A-compliant PDFs, this at
least prevents it from removing compliance on already compliant files.
Write the first pass of linearization to the named file. The resulting file is not a valid PDF file. This option is useful
only for debugging QPDFWriter's linearization code. When qpdf linearizes files, it writes the file in two passes,
using the first pass to calculate sizes and offsets that are required for hint tables and the linearization dictionary.
Ordinarily, the first pass is discarded. This option enables it to be captured.
When a page's contents are split across multiple streams, this option causes qpdf to combine them into a single
stream. Use of this option is never necessary for ordinary usage, but it can help when working with some files in
some cases. For example, some PDF writers split page contents into small streams at arbitrary points that may fall
in the middle of lexical tokens within the content, and some PDF readers may get confused on such files. If you
use qpdf to coalesce the content streams, such readers may be able to work with the file more easily. This can also
be combined with QDF mode or content normalization to make it easier to look at all of a page's contents at once.
This option collapses annotations into the pages' contents with special handling for form fields. Ordinarily, an
annotation is rendered separately and on top of the page. Combining annotations into the page's contents effectively
freezes the placement of the annotations, making them look right after various page transformations. The library
functionality backing this option was added for the benefit of programs that want to create n-up page layouts and
other similar things that don't work well with annotations. The option parameter may be any of the following:
• all: include all annotations that are not marked invisible or hidden
• print: only include annotations that indicate that they should appear when the page is printed
• screen: omit annotations that indicate they should not appear on the screen
Note that form fields are special because the annotations that are used to render filled-in form fields may become
out of date from the fields' values if the form is filled in by a program that doesn't know how to update the
appearances. If qpdf detects this case, its default behavior is not to flatten those annotations because doing so
would cause the value of the form field to be lost. This gives you a chance to go back and resave the form with a
program that knows how to generate appearances. QPDF itself can generate appearances with some limitations.
See the --generate-appearances option below.
If a file contains interactive form fields and indicates that the appearances are out of date with the values of the
form, this flag will regenerate appearances, subject to a few limitations. Note that there is not usually a reason to
do this, but it can be necessary before using the --flatten-annotations option. Most of these are not a problem
with well-behaved PDF files. The limitations are as follows:
• Radio button and checkbox appearances use the pre-set values in the PDF file. QPDF just makes sure that the
correct appearance is displayed based on the value of the field. This is fine for PDF files that create their forms


Running QPDF

properly. Some PDF writers save appearances for fields when they change, which could cause some controls
to have inconsistent appearances.
• For text fields and list boxes, any characters that fall outside of US-ASCII or, if detected, “Windows ANSI” or
“Mac Roman” encoding, will be replaced by the ? character.
• Quadding is ignored. Quadding is used to specify whether the contents of a field should be left, center, or right
aligned with the field.
• Rich text, multi-line, and other more elaborate formatting directives are ignored.
• There is no support for multi-select fields or signature fields.
If qpdf doesn't do a good enough job with your form, use an external application to save your filled-in form before
processing it with qpdf.
This flag causes qpdf to recompress all images that are not compressed with DCT (JPEG) using DCT compression
as long as doing so decreases the size in bytes of the image data and the image does not fall below minimum
specified dimensions. Useful information is provided when used in combination with --verbose. See also the -oi-min-width, --oi-min-height, and --oi-min-area options.
Avoid optimizing images whose width is below the specified amount. If omitted, the default is 128 pixels. Use
0 for no minimum.
Avoid optimizing images whose height is below the specified amount. If omitted, the default is 128 pixels. Use
0 for no minimum.
Avoid optimizing images whose pixel count (width × height) is below the specified amount. If omitted, the default
is 16,384 pixels. Use 0 for no minimum.
Turns on QDF mode. For additional information on QDF, please see Chapter 4, QDF Mode, page 19.
Forces the PDF version of the output file to be at least version. In other words, if the input file has a lower
version than the specified version, the specified version will be used. If the input file has a higher version, the
input file's original version will be used. It is seldom necessary to use this option since qpdf will automatically
increase the version as needed when adding features that require newer PDF readers.
The version number may be expressed in the form major.minor.extension-level, in which case the
version is interpreted as major.minor at extension level extension-level. For example, version 1.7.8
represents version 1.7 at extension level 8. Note that minimal syntax checking is done on the command line.
This option forces the PDF version to be the exact version specified even when the file may have content that
is not supported in that version. The version number is interpreted in the same way as with --min-version so
that extension levels can be set. In some cases, forcing the output file's PDF version to be lower than that of the
input file will cause qpdf to disable certain features of the document. Specifically, 256-bit keys are disabled if


Running QPDF

the version is less than 1.7 with extension level 8 (except R5 is disabled if less than 1.7 with extension level 3),
AES encryption is disabled if the version is less than 1.6, cleartext metadata and object streams are disabled if less
than 1.5, 128-bit encryption keys are disabled if less than 1.4, and all encryption is disabled if less than 1.3. Even
with these precautions, qpdf won't be able to do things like eliminate use of newer image compression schemes,
transparency groups, or other features that may have been added in more recent versions of PDF.
As a general rule, with the exception of big structural things like the use of object streams or AES encryption,
PDF viewers are supposed to ignore features in files that they don't support from newer versions. This means that
forcing the version to a lower version may make it possible to open your PDF file with an older version, though
bear in mind that some of the original document's functionality may be lost.
By default, when a stream is encoded using non-lossy filters that qpdf understands and is not already compressed
using a good compression scheme, qpdf will uncompress and recompress streams. Assuming proper filter implements,
this is safe and generally results in smaller files. This behavior may also be explicitly requested with --stream-data=compress.
When --normalize-content=y is specified, qpdf will attempt to normalize whitespace and newlines in page content
streams. This is generally safe but could, in some cases, cause damage to the content streams. This option is intended
for people who wish to study PDF content streams or to debug PDF content. You should not use this for “production”
PDF files.
This paragraph discusses edge cases of content normalization that are not of concern to most users and are not relevant
when content normalization is not enabled. When normalizing content, if qpdf runs into any lexical errors, it will print
a warning indicating that content may be damaged. The only situation in which qpdf is known to cause damage during
content normalization is when a page's contents are split across multiple streams and streams are split in the middle
of a lexical token such as a string, name, or inline image. There may be some pathological cases in which qpdf could
damage content without noticing this, such as if the partial tokens at the end of one stream and the beginning of the next
stream are both valid, but usually qpdf will be able to detect this case. For slightly increased safety, you can specify -coalesce-contents in addition to --normalize-content or --qdf. This will cause qpdf to combine all the content streams
into one, thus recombining any split tokens. However doing this will prevent you from being able to see the original
layout of the content streams. If you must inspect the original content streams in an uncompressed format, you can
always run with --qdf --normalize-content=n for a QDF file without content normalization, or alternatively --streamdata=uncompress for a regular non-QDF mode file with uncompressed streams. These will both uncompress all the
streams but will not attempt to normalize content. Please note that if you are using content normalization or QDF mode
for the purpose of manually inspecting files, you don't have to care about this.
Object streams, also known as compressed objects, were introduced into the PDF specification at version 1.5, corresponding to Acrobat 6. Some older PDF viewers may not support files with object streams. qpdf can be used to transform files with object streams to files without object streams or vice versa. As mentioned above, there are three object
stream modes: preserve, disable, and generate.
In preserve mode, the relationship to objects and the streams that contain them is preserved from the original file. In
disable mode, all objects are written as regular, uncompressed objects. The resulting file should be readable by older
PDF viewers. (Of course, the content of the files may include features not supported by older viewers, but at least
the structure will be supported.) In generate mode, qpdf will create its own object streams. This will usually result in
more compact PDF files, though they may not be readable by older viewers. In this mode, qpdf will also make sure
the PDF version number in the header is at least 1.5.
The --qdf flag turns on QDF mode, which changes some of the defaults described above. Specifically, in QDF mode,
by default, stream data is uncompressed, content streams are normalized, and encryption is removed. These defaults
can still be overridden by specifying the appropriate options as described above. Additionally, in QDF mode, stream
lengths are stored as indirect objects, objects are laid out in a less efficient but more readable fashion, and the documents
are interspersed with comments that make it easier for the user to find things and also make it possible for fix-qdf to
work properly. QDF mode is intended for people, mostly developers, who wish to inspect or modify PDF files in a
text editor. For details, please see Chapter 4, QDF Mode, page 19.


Running QPDF

3.8. Testing, Inspection, and Debugging Options
These options can be useful for digging into PDF files or for use in automated test suites for software that uses the qpdf
library. When any of the options in this section are specified, no output file should be given. The following options
are available:
Causes generation of a deterministic value for /ID. This prevents use of timestamp and output file name information in the /ID generation. Instead, at some slight additional runtime cost, the /ID field is generated to include a
digest of the significant parts of the content of the output PDF file. This means that a given qpdf operation should
generate the same /ID each time it is run, which can be useful when caching results or for generation of some test
data. Use of this flag is not compatible with creation of encrypted files.
Causes generation of a fixed value for /ID. This is intended for testing only. Never use it for production files. If
you are trying to get the same /ID each time for a given file and you are not generating encrypted files, consider
using the --deterministic-id option.
Causes use of a static initialization vector for AES-CBC. This is intended for testing only so that output files
can be reproducible. Never use it for production files. This option in particular is not secure since it significantly
weakens the encryption.
Suppresses inclusion of original object ID comments in QDF files. This can be useful when generating QDF files
for test purposes, particularly when comparing them to determine whether two PDF files have identical content.
Shows document encryption parameters. Also shows the document's user password if the owner password is given.
When encryption information is being displayed, as when --check or --show-encryption is given, display the
computed or retrieved encryption key as a hexadecimal string. This value is not ordinarily useful to users, but it
can be used as the argument to --password if the --password-is-hex-key is specified. Note that, when PDF files
are encrypted, passwords and other metadata are used only to compute an encryption key, and the encryption key
is what is actually used for encryption. This enables retrieval of that key.
Checks file integrity and linearization status.
Checks and displays all data in the linearization hint tables.
Shows the contents of the cross-reference table in a human-readable form. This is especially useful for files with
cross-reference streams which are stored in a binary format.


Running QPDF

Show the contents of the given object. This is especially useful for inspecting objects that are inside of object
streams (also known as “compressed objects”).
When used along with the --show-object option, if the object is a stream, shows the raw stream data instead of
object's contents.
When used along with the --show-object option, if the object is a stream, shows the filtered stream data instead
of object's contents. If the stream is filtered using filters that qpdf does not support, an error will be issued.
Prints the number of pages in the input file on a line by itself. Since the number of pages appears by itself on a
line, this option can be useful for scripting if you need to know the number of pages in a file.
Shows the object and generation number for each page dictionary object and for each content stream associated
with the page. Having this information makes it more convenient to inspect objects from a particular page.
When used along with --show-pages, also shows the object and generation numbers for the image objects on each
page. (At present, information about images in shared resource dictionaries are not output by this command. This
is discussed in a comment in the source code.)
Generate a JSON representation of the file. This is described in depth in Chapter 6, QPDF JSON, page 22
Describe the format of the JSON output.
This option is repeatable. If specified, only top-level keys specified will be included in the JSON output. If not
specified, all keys will be shown.
This option is repeatable. If specified, only specified objects will be shown in the “objects” key of the JSON
output. If absent, all objects will be shown.
Checks file structure and well as encryption, linearization, and encoding of stream data. A file for which --check
reports no errors may still have errors in stream data content but should otherwise be structurally sound. If --check
any errors, qpdf will exit with a status of 2. There are some recoverable conditions that --check detects. These
are issued as warnings instead of errors. If qpdf finds no errors but finds warnings, it will exit with a status of
3 (as of version 2.0.4). When --check is combined with other options, checks are always performed before any
other options are processed. For erroneous files, --check will cause qpdf to attempt to recover, after which other


Running QPDF

options are effectively operating on the recovered file. Combining --check with other options in this way can be
useful for manually recovering severely damaged files.
The --raw-stream-data and --filtered-stream-data options are ignored unless --show-object is given. Either of these
options will cause the stream data to be written to standard output. In order to avoid commingling of stream data with
other output, it is recommend that these objects not be combined with other test/inspection options.
If --filtered-stream-data is given and --normalize-content=y is also given, qpdf will attempt to normalize the stream
data as if it is a page content stream. This attempt will be made even if it is not a page content stream, in which case
it will produce unusable results.


Chapter 4. QDF Mode
In QDF mode, qpdf creates PDF files in what we call QDF form. A PDF file in QDF form, sometimes called a QDF
file, is a completely valid PDF file that has %QDF-1.0 as its third line (after the pdf header and binary characters)
and has certain other characteristics. The purpose of QDF form is to make it possible to edit PDF files, with some
restrictions, in an ordinary text editor. This can be very useful for experimenting with different PDF constructs or for
making one-off edits to PDF files (though there are other reasons why this may not always work).
It is ordinarily very difficult to edit PDF files in a text editor for two reasons: most meaningful data in PDF files is
compressed, and PDF files are full of offset and length information that makes it hard to add or remove data. A QDF
file is organized in a manner such that, if edits are kept within certain constraints, the fix-qdf program, distributed with
qpdf, is able to restore edited files to a correct state. The fix-qdf program takes no command-line arguments. It reads
a possibly edited QDF file from standard input and writes a repaired file to standard output.
The following attributes characterize a QDF file:
• All objects appear in numerical order in the PDF file, including when objects appear in object streams.
• Objects are printed in an easy-to-read format, and all line endings are normalized to UNIX line endings.
• Unless specifically overridden, streams appear uncompressed (when qpdf supports the filters and they are compressed with a non-lossy compression scheme), and most content streams are normalized (line endings are converted
to just a UNIX-style linefeeds).
• All streams lengths are represented as indirect objects, and the stream length object is always the next object after
the stream. If the stream data does not end with a newline, an extra newline is inserted, and a special comment
appears after the stream indicating that this has been done.
• If the PDF file contains object streams, if object stream n contains k objects, those objects are numbered from n
+1 through n+k, and the object number/offset pairs appear on a separate line for each object. Additionally, each
object in the object stream is preceded by a comment indicating its object number and index. This makes it very
easy to find objects in object streams.
• All beginnings of objects, stream tokens, endstream tokens, and endobj tokens appear on lines by themselves.
A blank line follows every endobj token.
• If there is a cross-reference stream, it is unfiltered.
• Page dictionaries and page content streams are marked with special comments that make them easy to find.
• Comments precede each object indicating the object number of the corresponding object in the original file.
When editing a QDF file, any edits can be made as long as the above constraints are maintained. This means that you
can freely edit a page's content without worrying about messing up the QDF file. It is also possible to add new objects
so long as those objects are added after the last object in the file or subsequent objects are renumbered. If a QDF file
has object streams in it, you can always add the new objects before the xref stream and then change the number of the
xref stream, since nothing generally ever references it by number.
It is not generally practical to remove objects from QDF files without messing up object numbering, but if you remove
all references to an object, you can run qpdf on the file (after running fix-qdf), and qpdf will omit the now-orphaned
When fix-qdf is run, it goes through the file and recomputes the following parts of the file:
• the /N, /W, and /First keys of all object stream dictionaries


QDF Mode

• the pairs of numbers representing object numbers and offsets of objects in object streams
• all stream lengths
• the cross-reference table or cross-reference stream
• the offset to the cross-reference table or cross-reference stream following the startxref token


Chapter 5. Using the QPDF Library
5.1. Using QPDF from C++
The source tree for the qpdf package has an examples directory that contains a few example programs. The qpdf/
qpdf.cc source file also serves as a useful example since it exercises almost all of the qpdf library's public interface.
The best source of documentation on the library itself is reading comments in include/qpdf/QPDF.hh, include/qpdf/
QPDFWriter.hh, and include/qpdf/QPDFObjectHandle.hh.
All header files are installed in the include/qpdf directory. It is recommend that you use #include  rather than adding include/qpdf to your include path.
When linking against the qpdf static library, you may also need to specify -lz -ljpeg on your link command. If
your system understands how to read libtool .la files, this may not be necessary.
The qpdf library is safe to use in a multithreaded program, but no individual QPDF object instance (including QPDF,
QPDFObjectHandle, or QPDFWriter) can be used in more than one thread at a time. Multiple threads may
simultaneously work with different instances of these and all other QPDF objects.

5.2. Using QPDF from other languages
The qpdf library is implemented in C++, which makes it hard to use directly in other languages. There are a few things
that can help.
The qpdf library includes a “C” language interface that provides a subset of the overall capabilities. The header
file qpdf/qpdf-c.h includes information about its use. As long as you use a C++ linker, you can link C programs
with qpdf and use the C API. For languages that can directly load methods from a shared library, the C API can
also be useful. People have reported success using the C API from other languages on Windows by directly calling
functions in the DLL.
A Python module called pikepdf [https://pypi.org/project/pikepdf/] provides a clean and highly functional set of
Python bindings to the qpdf library. Using pikepdf, you can work with PDF files in a natural way and combine
qpdf's capabilities with other functionality provided by Python's rich standard library and available modules.
Other Languages
Starting with version 8.3.0, the qpdf command-line tool can produce a JSON representation of the PDF file's
non-content data. This can facilitate interacting programmatically with PDF files through qpdf's command line
interface. For more information, please see Chapter 6, QPDF JSON, page 22.


Chapter 6. QPDF JSON
6.1. Overview
Beginning with qpdf version 8.3.0, the qpdf command-line program can produce a JSON representation of the noncontent data in a PDF file. It includes a dump in JSON format of all objects in the PDF file excluding the content
of streams. This JSON representation makes it very easy to look in detail at the structure of a given PDF file, and it
also provides a great way to work with PDF files programmatically from the command-line in languages that can't
call or link with the qpdf library directly. Note that stream data can be extracted from PDF files using other qpdf
command-line options.

6.2. JSON Guarantees
The qpdf JSON representation includes a JSON serialization of the raw objects in the PDF file as well as some computed information in a more easily extracted format. QPDF provides some guarantees about its JSON format. These
guarantees are designed to simplify the experience of a developer working with the JSON format.
The top-level JSON object output is a dictionary. The JSON output contains various nested dictionaries and arrays.
With the exception of dictionaries that are populated by the fields of objects from the file, all instances of a
dictionary are guaranteed to have exactly the same keys. Future versions of qpdf are free to add additional keys
but not to remove keys or change the type of object that a key points to. The qpdf program validates this guarantee,
and in the unlikely event that a bug in qpdf should cause it to generate data that doesn't conform to this rule, it
will ask you to file a bug report.
The top-level JSON structure contains a “version” key whose value is simple integer. The value of the version key will be incremented if a non-compatible change is made. A non-compatible change would be any
change that involves removal of a key, a change to the format of data pointed to by a key, or a semantic change
that requires a different interpretation of a previously existing key. A strong effort will be made to avoid breaking
The qpdf command can be invoked with the --json-help option. This will output a JSON structure that has the
same structure as the JSON output that qpdf generates, except that each field in the help output is a description of
the corresponding field in the JSON output. The specific guarantees are as follows:
• A dictionary in the help output means that the corresponding location in the actual JSON output is also a
dictionary with exactly the same keys; that is, no keys present in help are absent in the real output, and no keys
will be present in the real output that are not in help.
• A string in the help output is a description of the item that appears in the corresponding location of the actual
output. The corresponding output can have any format.
• An array in the help output always contains a single element. It indicates that the corresponding location in the
actual output is also an array, and that each element of the array has whatever format is implied by the single
element of the help output's array.
For example, the help output indicates includes a “pagelabels” key whose value is an array of one element.
That element is a dictionary with keys “index” and “label”. In addition to describing the meaning of those
keys, this tells you that the actual JSON output will contain a pagelabels array, each of whose elements is a
dictionary that contains an index key, a label key, and no other keys.



Directness and Simplicity
The JSON output contains the value of every object in the file, but it also contains some processed data. This
is analogous to how qpdf's library interface works. The processed data is similar to the helper functions in that
it allows you to look at certain aspects of the PDF file without having to understand all the nuances of the PDF
specification, while the raw objects allow you to mine the PDF for anything that the higher-level interfaces are

6.3. Limitations of JSON Representation
There are a few limitations to be aware of with the JSON structure:
• Strings, names, and indirect object references in the original PDF file are all converted to strings in the JSON
representation. In the case of a “normal” PDF file, you can tell the difference because a name starts with a slash (/),
and an indirect object reference looks like n n R, but if there were to be a string that looked like a name or indirect
object reference, there would be no way to tell this from the JSON output. Note that there are certain cases where
you know for sure what something is, such as knowing that dictionary keys in objects are always names and that
certain things in the higher-level computed data are known to contain indirect object references.
• The JSON format doesn't support binary data very well. Mostly the details are not important, but they are presented
here for information. When qpdf outputs a string in the JSON representation, it converts the string to UTF-8, assuming usual PDF string semantics. Specifically, if the original string is UTF-16, it is converted to UTF-8. Otherwise, it
is assumed to have PDF doc encoding, and is converted to UTF-8 with that assumption. This causes strange things
to happen to binary strings. For example, if you had the binary string <038051>, this would be output to the JSON
as \u0003•Q because 03 is not a printable character and 80 is the bullet character in PDF doc encoding and is
mapped to the Unicode value 2022. Since 51 is Q, it is output as is. If you wanted to convert back from here to
a binary string, would have to recognize Unicode values whose code points are higher than 0xFF and map those
back to their corresponding PDF doc encoding characters. There is no way to tell the difference between a Unicode
string that was originally encoded as UTF-16 or one that was converted from PDF doc encoding. In other words,
it's best if you don't try to use the JSON format to extract binary strings from the PDF file, but if you really had
to, it could be done. Note that qpdf's --show-object option does not have this limitation and will reveal the string
as encoded in the original file.

6.4. JSON: Special Considerations
For the most part, the built-in JSON help tells you everything you need to know about the JSON format, but there are
a few non-obvious things to be aware of:
• While qpdf guarantees that keys present in the help will be present in the output, those fields may be null or empty
if the information is not known or absent in the file. Also, if you specify --json-keys, the keys that are not listed will
be excluded entirely except for those that --json-help says are always present.
• In a few places, there are keys with names containing pageposfrom1. The values of these keys are null or an
integer. If an integer, they point to a page index within the file numbering from 1. Note that JSON indexes from 0,
and you would also use 0-based indexing using the API. However, 1-based indexing is easier in this case because
the command-line syntax for specifying page ranges is 1-based. If you were going to write a program that looked
through the JSON for information about specific pages and then use the command-line to extract those pages, 1based indexing is easier. Besides, it's more convenient to subtract 1 from a program in a real programming language
than it is to add 1 from shell code.
• The image information included in the page section of the JSON output includes the key “filterable”. Note
that the value of this field may depend on the --decode-level that you invoke qpdf with. The JSON output includes
a top-level key “parameters” that indicates the decode level used for computing whether a stream was filterable.



For example, jpeg images will be shown as not filterable by default, but they will be shown as filterable if you run
qpdf --json --decode-level=all.


Chapter 7. Design and Library Notes
7.1. Introduction
This section was written prior to the implementation of the qpdf package and was subsequently modified to reflect the
implementation. In some cases, for purposes of explanation, it may differ slightly from the actual implementation. As
always, the source code and test suite are authoritative. Even if there are some errors, this document should serve as
a road map to understanding how this code works.
In general, one should adhere strictly to a specification when writing but be liberal in reading. This way, the product
of our software will be accepted by the widest range of other programs, and we will accept the widest range of input
files. This library attempts to conform to that philosophy whenever possible but also aims to provide strict checking
for people who want to validate PDF files. If you don't want to see warnings and are trying to write something that
is tolerant, you can call setSuppressWarnings(true). If you want to fail on the first error, you can call setAttemptRecovery(false). The default behavior is to generating warnings for recoverable problems. Note that
recovery will not always produce the desired results even if it is able to get through the file. Unlike most other PDF
files that produce generic warnings such as “This file is damaged,”, qpdf generally issues a detailed error message that
would be most useful to a PDF developer. This is by design as there seems to be a shortage of PDF validation tools
out there. This was, in fact, one of the major motivations behind the initial creation of qpdf.

7.2. Design Goals
The QPDF package includes support for reading and rewriting PDF files. It aims to hide from the user details involving
object locations, modified (appended) PDF files, the directness/indirectness of objects, and stream filters including
encryption. It does not aim to hide knowledge of the object hierarchy or content stream contents. Put another way, a
user of the qpdf library is expected to have knowledge about how PDF files work, but is not expected to have to keep
track of bookkeeping details such as file positions.
A user of the library never has to care whether an object is direct or indirect, though it is possible to determine whether
an object is direct or not if this information is needed. All access to objects deals with this transparently. All memory
management details are also handled by the library.
The PointerHolder object is used internally by the library to deal with memory management. This is basically a
smart pointer object very similar in spirit to C++-11's std::shared_ptr object, but predating it by several years. This
library also makes use of a technique for giving fine-grained access to methods in one class to other classes by using
public subclasses with friends and only private members that in turn call private methods of the containing class. See
QPDFObjectHandle::Factory as an example.
The top-level qpdf class is QPDF. A QPDF object represents a PDF file. The library provides methods for both
accessing and mutating PDF files.
The primary class for interacting with PDF objects is QPDFObjectHandle. Instances of this class can be passed
around by value, copied, stored in containers, etc. with very low overhead. Instances of QPDFObjectHandle created
by reading from a file will always contain a reference back to the QPDF object from which they were created. A
QPDFObjectHandle may be direct or indirect. If indirect, the QPDFObject the PointerHolder initially points to
is a null pointer. In this case, the first attempt to access the underlying QPDFObject will result in the QPDFObject
being resolved via a call to the referenced QPDF instance. This makes it essentially impossible to make coding errors
in which certain things will work for some PDF files and not for others based on which objects are direct and which
objects are indirect.
Instances of QPDFObjectHandle can be directly created and modified using static factory methods in the QPDFObjectHandle class. There are factory methods for each type of object as well as a convenience method QPDFObjec-


Design and Library Notes

tHandle::parse that creates an object from a string representation of the object. Existing instances of QPDFObjectHandle can also be modified in several ways. See comments in QPDFObjectHandle.hh for details.
An instance of QPDF is constructed by using the class's default constructor. If desired, the QPDF object may be
configured with various methods that change its default behavior. Then the QPDF::processFile() method is passed
the name of a PDF file, which permanently associates the file with that QPDF object. A password may also be given
for access to password-protected files. QPDF does not enforce encryption parameters and will treat user and owner
passwords equivalently. Either password may be used to access an encrypted file. 1 QPDF will allow recovery of a
user password given an owner password. The input PDF file must be seekable. (Output files written by QPDFWriter
need not be seekable, even when creating linearized files.) During construction, QPDF validates the PDF file's header,
and then reads the cross reference tables and trailer dictionaries. The QPDF class keeps only the first trailer dictionary
though it does read all of them so it can check the /Prev key. QPDF class users may request the root object and
the trailer dictionary specifically. The cross reference table is kept private. Objects may then be requested by number
of by walking the object tree.
When a PDF file has a cross-reference stream instead of a cross-reference table and trailer, requesting the document's
trailer dictionary returns the stream dictionary from the cross-reference stream instead.
There are some convenience routines for very common operations such as walking the page tree and returning a vector
of all page objects. For full details, please see the header files QPDF.hh and QPDFObjectHandle.hh. There are also
some additional helper classes that provide higher level API functions for certain document constructions. These are
discussed in Section 7.3, “Helper Classes”, page 26.

7.3. Helper Classes
QPDF version 8.1 introduced the concept of helper classes. Helper classes are intended to contain higher level APIs that
allow developers to work with certain document constructs at an abstraction level above that of QPDFObjectHandle
while staying true to qpdf's philosophy of not hiding document structure from the developer. As with qpdf in general,
the goal is take away some of the more tedious bookkeeping aspects of working with PDF files, not to remove the need
for the developer to understand how the PDF construction in question works. The driving factor behind the creation
of helper classes was to allow the evolution of higher level interfaces in qpdf without polluting the interfaces of the
main top-level classes QPDF and QPDFObjectHandle.
There are two kinds of helper classes: document helpers and object helpers. Document helpers are constructed with a
reference to a QPDF object and provide methods for working with structures that are at the document level. Object
helpers are constructed with an instance of a QPDFObjectHandle and provide methods for working with specific
types of objects.
Examples of document helpers include QPDFPageDocumentHelper, which contains methods for operating on the
document's page trees, such as enumerating all pages of a document and adding and removing pages; and QPDFAcroFormDocumentHelper, which contains document-level methods related to interactive forms, such as enumerating
form fields and creating mappings between form fields and annotations.
Examples of object helpers include QPDFPageObjectHelper for performing operations on pages such as page
rotation and some operations on content streams, QPDFFormFieldObjectHelper for performing operations related
to interactive form fields, and QPDFAnnotationObjectHelper for working with annotations.
It is always possible to retrieve the underlying QPDF reference from a document helper and the underlying QPDFObjectHandle reference from an object helper. Helpers are designed to be helpers, not wrappers. The intention is that,
in general, it is safe to freely intermix operations that use helpers with operations that use the underlying objects.
Document and object helpers do not attempt to provide a complete interface for working with the things they are

As pointed out earlier, the intention is not for qpdf to be used to bypass security on files. but as any open source PDF consumer may be easily
modified to bypass basic PDF document security, and qpdf offers may transformations that can do this as well, there seems to be little point in the
added complexity of conditionally enforcing document security.


Design and Library Notes

helping with, nor do they attempt to encapsulate underlying structures. They just provide a few methods to help with
error-prone, repetitive, or complex tasks. In some cases, a helper object may cache some information that is expensive
to gather. In such cases, the helper classes are implemented so that their own methods keep the cache consistent, and
the header file will provide a method to invalidate the cache and a description of what kinds of operations would make
the cache invalid. If in doubt, you can always discard a helper class and create a new one with the same underlying
objects, which will ensure that you have discarded any stale information.
By Convention, document helpers are called QPDFSomethingDocumentHelper and are derived from QPDFDocumentHelper, and object helpers are called QPDFSomethingObjectHelper and are derived from QPDFObjectHelper. For details on specific helpers, please see their header files. You can find them by looking at include/qpdf/
QPDF*DocumentHelper.hh and include/qpdf/QPDF*ObjectHelper.hh.
In order to avoid creation of circular dependencies, the following general guidelines are followed with helper classes:
• Core class interfaces do not know about helper classes. For example, no methods of QPDF or QPDFObjectHandle
will include helper classes in their interfaces.
• Interfaces of object helpers will usually not use document helpers in their interfaces. This is because it is much more
useful for document helpers to have methods that return object helpers. Most operations in PDF files start at the
document level and go from there to the object level rather than the other way around. It can sometimes be useful
to map back from object-level structures to document-level structures. If there is a desire to do this, it will generally
be provided by a method in the document helper class.
• Most of the time, object helpers don't know about other object helpers. However, in some cases, one type of object
may be a container for another type of object, in which case it may make sense for the outer object to know about the
inner object. For example, there are methods in the QPDFPageObjectHelper that know QPDFAnnotationObjectHelper because references to annotations are contained in page dictionaries.
• Any helper or core library class may use helpers in their implementations.
Prior to qpdf version 8.1, higher level interfaces were added as “convenience functions” in either QPDF or QPDFObjectHandle. For compatibility, older convenience functions for operating with pages will remain in those classes
even as alternatives are provided in helper classes. Going forward, new higher level interfaces will be provided using
helper classes.

7.4. Implementation Notes
This section contains a few notes about QPDF's internal implementation, particularly around what it does when it first
processes a file. This section is a bit of a simplification of what it actually does, but it could serve as a starting point
to someone trying to understand the implementation. There is nothing in this section that you need to know to use
the qpdf library.
QPDFObject is the basic PDF Object class. It is an abstract base class from which are derived classes for each type
of PDF object. Clients do not interact with Objects directly but instead interact with QPDFObjectHandle.
When the QPDF class creates a new object, it dynamically allocates the appropriate type of QPDFObject and immediately hands the pointer to an instance of QPDFObjectHandle. The parser reads a token from the current file
position. If the token is a not either a dictionary or array opener, an object is immediately constructed from the single
token and the parser returns. Otherwise, the parser iterates in a special mode in which it accumulates objects until it
finds a balancing closer. During this process, the “R” keyword is recognized and an indirect QPDFObjectHandle
may be constructed.
The QPDF::resolve() method, which is used to resolve an indirect object, may be invoked from the QPDFObjectHandle class. It first checks a cache to see whether this object has already been read. If not, it reads the object from
the PDF file and caches it. It the returns the resulting QPDFObjectHandle. The calling object handle then replaces


Design and Library Notes

its PointerHolder with the one from the newly returned QPDFObjectHandle. In this way, only a
single copy of any direct object need exist and clients can access objects transparently without knowing caring whether
they are direct or indirect objects. Additionally, no object is ever read from the file more than once. That means that
only the portions of the PDF file that are actually needed are ever read from the input file, thus allowing the qpdf
package to take advantage of this important design goal of PDF files.
If the requested object is inside of an object stream, the object stream itself is first read into memory. Then the tokenizer
reads objects from the memory stream based on the offset information stored in the stream. Those individual objects
are cached, after which the temporary buffer holding the object stream contents are discarded. In this way, the first
time an object in an object stream is requested, all objects in the stream are cached.
The following example should clarify how QPDF processes a simple file.
• Client constructs QPDF pdf and calls pdf.processFile("a.pdf");.
• The QPDF class checks the beginning of a.pdf for a PDF header. It then reads the cross reference table mentioned
at the end of the file, ensuring that it is looking before the last %%EOF. After getting to trailer keyword, it
invokes the parser.
• The parser sees “<<”, so it calls itself recursively in dictionary creation mode.
• In dictionary creation mode, the parser keeps accumulating objects until it encounters “>>”. Each object that is
read is pushed onto a stack. If “R” is read, the last two objects on the stack are inspected. If they are integers,
they are popped off the stack and their values are used to construct an indirect object handle which is then pushed
onto the stack. When “>>” is finally read, the stack is converted into a QPDF_Dictionary which is placed in a
QPDFObjectHandle and returned.
• The resulting dictionary is saved as the trailer dictionary.
• The /Prev key is searched. If present, QPDF seeks to that point and repeats except that the new trailer dictionary
is not saved. If /Prev is not present, the initial parsing process is complete.
If there is an encryption dictionary, the document's encryption parameters are initialized.
• The client requests root object. The QPDF class gets the value of root key from trailer dictionary and returns it. It
is an unresolved indirect QPDFObjectHandle.
• The client requests the /Pages key from root QPDFObjectHandle. The QPDFObjectHandle notices that it
is indirect so it asks QPDF to resolve it. QPDF looks in the object cache for an object with the root dictionary's
object ID and generation number. Upon not seeing it, it checks the cross reference table, gets the offset, and reads
the object present at that offset. It stores the result in the object cache and returns the cached result. The calling
QPDFObjectHandle replaces its object pointer with the one from the resolved QPDFObjectHandle, verifies
that it a valid dictionary object, and returns the (unresolved indirect) QPDFObject handle to the top of the Pages
As the client continues to request objects, the same process is followed for each new requested object.

7.5. Casting Policy
This section describes the casting policy followed by qpdf's implementation. This is no concern to qpdf's end users
and largely of no concern to people writing code that uses qpdf, but it could be of interest to people who are porting
qpdf to a new platform or who are making modifications to the code.
The C++ code in qpdf is free of old-style casts except where unavoidable (e.g. where the old-style cast is in a macro
provided by a third-party header file). When there is a need for a cast, it is handled, in order of preference, by rewriting
the code to avoid the need for a cast, calling const_cast, calling static_cast, calling reinterpret_cast, or calling some


Design and Library Notes

combination of the above. As a last resort, a compiler-specific #pragma may be used to suppress a warning that we
don't want to fix. Examples may include suppressing warnings about the use of old-style casts in code that is shared
between C and C++ code.
The casting policy explicitly prohibits casting between integer sizes for no purpose other than to quiet a compiler
warning when there is no reasonable chance of a problem resulting. The reason for this exclusion is that the practice
of adding these additional casts precludes future use of additional compiler warnings as a tool for making future
improvements to this aspect of the code, and it also damages the readability of the code.
There are a few significant areas where casting is common in the qpdf sources or where casting would be required to
quiet higher levels of compiler warnings but is omitted at present:
• char vs. unsigned char. For historical reasons, there are a lot of places in qpdf's internals that deal with
unsigned char, which means that a lot of casting is required to interoperate with standard library calls and
std::string. In retrospect, qpdf should have probably used regular (signed) char and char* everywhere and
just cast to unsigned char when needed, but it's too late to make that change now. There are reinterpret_cast
calls to go between char* and unsigned char*, and there are static_cast calls to go between char and
unsigned char. These should always be safe.
• Non-const unsigned char* used in the Pipeline interface. The pipeline interface has a write call that uses
unsigned char* without a const qualifier. The main reason for this is to support pipelines that make calls to
third-party libraries, such as zlib, that don't include const in their interfaces. Unfortunately, there are many places
in the code where it is desirable to have const char* with pipelines. None of the pipeline implementations in
qpdf currently modify the data passed to write, and doing so would be counter to the intent of Pipeline, but there
is nothing in the code to prevent this from being done. There are places in the code where const_cast is used to
remove the const-ness of pointers going into Pipelines. This could theoretically be unsafe, but there is adequate
testing to assert that it is safe and will remain safe in qpdf's code.
• size_t vs. qpdf_offset_t. This is pretty much unavoidable since sizes are unsigned types and offsets are
signed types. Whenever it is necessary to seek by an amount given by a size_t, it becomes necessary to mix and
match between size_t and qpdf_offset_t. Additionally, qpdf sometimes treats memory buffers like files (as
with BufferInputSource, and those seek interfaces have to be consistent with file-based input sources. Neither
gcc nor MSVC give warnings for this case by default, but both have warning flags that can enable this. (MSVC:
/W14267 or /W3, which also enables some additional warnings that we ignore; gcc: -Wconversion -Wsign-conversion). This could matter for files whose sizes are larger than 263 bytes, but it is reasonable to expect that a world
where such files are common would also have larger size_t and qpdf_offset_t types in it. On most 64-bit
systems at the time of this writing (the release of version 4.1.0 of qpdf), both size_t and qpdf_offset_t are
64-bit integer types, while on many current 32-bit systems, size_t is a 32-bit type while qpdf_offset_t is a
64-bit type. I am not aware of any cases where 32-bit systems that have size_t smaller than qpdf_offset_t
could run into problems. Although I can't conclusively rule out the possibility of such problems existing, I suspect
any cases would be pretty contrived. In the event that someone should produce a file that qpdf can't handle because
of what is suspected to be issues involving the handling of size_t vs. qpdf_offset_t (such files may behave
properly on 64-bit systems but not on 32-bit systems because they have very large embedded files or streams, for
example), the above mentioned warning flags could be enabled and all those implicit conversions could be carefully
scrutinized. (I have already gone through that exercise once in adding support for files larger than 4 GB in size.) I
continue to be committed to supporting large files on 32-bit systems, but I would not go to any lengths to support
corner cases involving large embedded files or large streams that work on 64-bit systems but not on 32-bit systems
because of size_t being too small. It is reasonable to assume that anyone working with such files would be using
a 64-bit system anyway since many 32-bit applications would have similar difficulties.
• size_t vs. int or long. There are some cases where size_t and int or long or size_t and unsigned
int or unsigned long are used interchangeably. These cases occur when working with very small amounts of
memory, such as with the bit readers (where we're working with just a few bytes at a time), some cases of strlen, and
a few other cases. I have scrutinized all of these cases and determined them to be safe, but there is no mechanism in
the code to ensure that new unsafe conversions between int and size_t aren't introduced short of good testing


Design and Library Notes

and strong awareness of the issues. Again, if any such bugs are suspected in the future, enabling the additional
warning flags and scrutinizing the warnings would be in order.
To be clear, I believe qpdf to be well-behaved with respect to sizes and offsets, and qpdf's test suite includes actual
generation and full processing of files larger than 4 GB in size. The issues raised here are largely academic and should
not in any way be interpreted to mean that qpdf has practical problems involving sloppiness with integer types. I also
believe that appropriate measures have been taken in the code to avoid problems with signed vs. unsigned integers
from resulting in memory overwrites or other issues with potential security implications, though there are never any
absolute guarantees.

7.6. Encryption
Encryption is supported transparently by qpdf. When opening a PDF file, if an encryption dictionary exists, the QPDF
object processes this dictionary using the password (if any) provided. The primary decryption key is computed and
cached. No further access is made to the encryption dictionary after that time. When an object is read from a file, the
object ID and generation of the object in which it is contained is always known. Using this information along with
the stored encryption key, all stream and string objects are transparently decrypted. Raw encrypted objects are never
stored in memory. This way, nothing in the library ever has to know or care whether it is reading an encrypted file.
An interface is also provided for writing encrypted streams and strings given an encryption key. This is used by
QPDFWriter when it rewrites encrypted files.
When copying encrypted files, unless otherwise directed, qpdf will preserve any encryption in force in the original
file. qpdf can do this with either the user or the owner password. There is no difference in capability based on which
password is used. When 40 or 128 bit encryption keys are used, the user password can be recovered with the owner
password. With 256 keys, the user and owner passwords are used independently to encrypt the actual encryption key,
so while either can be used, the owner password can no longer be used to recover the user password.
Starting with version 4.0.0, qpdf can read files that are not encrypted but that contain encrypted attachments, but it
cannot write such files. qpdf also requires the password to be specified in order to open the file, not just to extract
attachments, since once the file is open, all decryption is handled transparently. When copying files like this while
preserving encryption, qpdf will apply the file's encryption to everything in the file, not just to the attachments. When
decrypting the file, qpdf will decrypt the attachments. In general, when copying PDF files with multiple encryption
formats, qpdf will choose the newest format. The only exception to this is that clear-text metadata will be preserved
as clear-text if it is that way in the original file.

7.7. Random Number Generation
QPDF generates random numbers to support generation of encrypted data. Versions prior to 5.0.1 used random or rand
from stdlib to generate random numbers. Version 5.0.1, if available, used operating system-provided secure random
number generation instead, enabling use of stdlib random number generation only if enabled by a compile-time option.
Starting in version 5.1.0, use of insecure random numbers was disabled unless enabled at compile time. Starting in
version 5.1.0, it is also possible for you to disable use of OS-provided secure random numbers. This is especially
useful on Windows if you want to avoid a dependency on Microsoft's cryptography API. In this case, you must provide
your own random data provider. Regardless of how you compile qpdf, starting in version 5.1.0, it is possible for you
to provide your own random data provider at runtime. This would enable you to use some software-based secure
pseudorandom number generator and to avoid use of whatever the operating system provides. For details on how to
do this, please refer to the top-level README.md file in the source distribution and to comments in QUtil.hh.

7.8. Adding and Removing Pages
While qpdf's API has supported adding and modifying objects for some time, version 3.0 introduces specific methods
for adding and removing pages. These are largely convenience routines that handle two tricky issues: pushing inher-


Design and Library Notes

itable resources from the /Pages tree down to individual pages and manipulation of the /Pages tree itself. For
details, see addPage and surrounding methods in QPDF.hh.

7.9. Reserving Object Numbers
Version 3.0 of qpdf introduced the concept of reserved objects. These are seldom needed for ordinary operations, but
there are cases in which you may want to add a series of indirect objects with references to each other to a QPDF object.
This causes a problem because you can't determine the object ID that a new indirect object will have until you add it to
the QPDF object with QPDF::makeIndirectObject. The only way to add two mutually referential objects to a QPDF
object prior to version 3.0 would be to add the new objects first and then make them refer to each other after adding
them. Now it is possible to create a reserved object using QPDFObjectHandle::newReserved. This is an indirect object
that stays “unresolved” even if it is queried for its type. So now, if you want to create a set of mutually referential
objects, you can create reservations for each one of them and use those reservations to construct the references. When
finished, you can call QPDF::replaceReserved to replace the reserved objects with the real ones. This functionality
will never be needed by most applications, but it is used internally by QPDF when copying objects from other PDF
files, as discussed in Section 7.10, “Copying Objects From Other PDF Files”, page 31. For an example of how to
use reserved objects, search for newReserved in test_driver.cc in qpdf's sources.

7.10. Copying Objects From Other PDF Files
Version 3.0 of qpdf introduced the ability to copy objects into a QPDF object from a different QPDF object, which
we refer to as foreign objects. This allows arbitrary merging of PDF files. The “from” QPDF object must remain valid
after the copy as discussed in the note below. The qpdf command-line tool provides limited support for basic page
selection, including merging in pages from other files, but the library's API makes it possible to implement arbitrarily
complex merging operations. The main method for copying foreign objects is QPDF::copyForeignObject. This takes
an indirect object from another QPDF and copies it recursively into this object while preserving all object structure,
including circular references. This means you can add a direct object that you create from scratch to a QPDF object with
QPDF::makeIndirectObject, and you can add an indirect object from another file with QPDF::copyForeignObject.
The fact that QPDF::makeIndirectObject does not automatically detect a foreign object and copy it is an explicit design
decision. Copying a foreign object seems like a sufficiently significant thing to do that it should be done explicitly.
The other way to copy foreign objects is by passing a page from one QPDF to another by calling QPDF::addPage.
In contrast to QPDF::makeIndirectObject, this method automatically distinguishes between indirect objects in the
current file, foreign objects, and direct objects.
Please note: when you copy objects from one QPDF to another, the source QPDF object must remain valid until you
have finished with the destination object. This is because the original object is still used to retrieve any referenced
stream data from the copied object.

7.11. Writing PDF Files
The qpdf library supports file writing of QPDF objects to PDF files through the QPDFWriter class. The QPDFWriter
class has two writing modes: one for non-linearized files, and one for linearized files. See Chapter 8, Linearization, page 34 for a description of linearization is implemented. This section describes how we write non-linearized
files including the creation of QDF files (see Chapter 4, QDF Mode, page 19.
This outline was written prior to implementation and is not exactly accurate, but it provides a correct “notional” idea
of how writing works. Look at the code in QPDFWriter for exact details.
• Initialize state:
• next object number = 1


Design and Library Notes

• object queue = empty
• renumber table: old object id/generation to new id/0 = empty
• xref table: new id -> offset = empty
• Create a QPDF object from a file.
• Write header for new PDF file.
• Request the trailer dictionary.
• For each value that is an indirect object, grab the next object number (via an operation that returns and increments
the number). Map object to new number in renumber table. Push object onto queue.
• While there are more objects on the queue:
• Pop queue.
• Look up object's new number n in the renumbering table.
• Store current offset into xref table.
• Write n 0 obj.
• If object is null, whether direct or indirect, write out null, thus eliminating unresolvable indirect object references.
• If the object is a stream stream, write stream contents, piped through any filters as required, to a memory buffer.
Use this buffer to determine the stream length.
• If object is not a stream, array, or dictionary, write out its contents.
• If object is an array or dictionary (including stream), traverse its elements (for array) or values (for dictionaries),
handling recursive dictionaries and arrays, looking for indirect objects. When an indirect object is found, if it is
not resolvable, ignore. (This case is handled when writing it out.) Otherwise, look it up in the renumbering table.
If not found, grab the next available object number, assign to the referenced object in the renumbering table, and
push the referenced object onto the queue. As a special case, when writing out a stream dictionary, replace length,
filters, and decode parameters as required.
Write out dictionary or array, replacing any unresolvable indirect object references with null (pdf spec says reference to non-existent object is legal and resolves to null) and any resolvable ones with references to the renumbered objects.
• If the object is a stream, write stream\n, the stream contents (from the memory buffer), and \nendstream\n.
• When done, write endobj.
Once we have finished the queue, all referenced objects will have been written out and all deleted objects or unreferenced objects will have been skipped. The new cross-reference table will contain an offset for every new object
number from 1 up to the number of objects written. This can be used to write out a new xref table. Finally we can
write out the trailer dictionary with appropriately computed /ID (see spec, 8.3, File Identifiers), the cross reference
table offset, and %%EOF.

7.12. Filtered Streams
Support for streams is implemented through the Pipeline interface which was designed for this package.


Design and Library Notes

When reading streams, create a series of Pipeline objects. The Pipeline abstract base requires implementation write()
and finish() and provides an implementation of getNext(). Each pipeline object, upon receiving data, does whatever it
is going to do and then writes the data (possibly modified) to its successor. Alternatively, a pipeline may be an endof-the-line pipeline that does something like store its output to a file or a memory buffer ignoring a successor. For
additional details, look at Pipeline.hh.
QPDF can read raw or filtered streams. When reading a filtered stream, the QPDF class creates a Pipeline object for
one of each appropriate filter object and chains them together. The last filter should write to whatever type of output
is required. The QPDF class has an interface to write raw or filtered stream contents to a given pipeline.


Chapter 8. Linearization
This chapter describes how QPDF and QPDFWriter implement creation and processing of linearized PDFS.

8.1. Basic Strategy for Linearization
To avoid the incestuous problem of having the qpdf library validate its own linearized files, we have a special linearized
file checking mode which can be invoked via qpdf --check-linearization (or qpdf --check). This mode reads the
linearization parameter dictionary and the hint streams and validates that object ordering, parameters, and hint stream
contents are correct. The validation code was first tested against linearized files created by external tools (Acrobat and
pdlin) and then used to validate files created by QPDFWriter itself.

8.2. Preparing For Linearization
Before creating a linearized PDF file from any other PDF file, the PDF file must be altered such that all page attributes
are propagated down to the page level (and not inherited from parents in the /Pages tree). We also have to know
which objects refer to which other objects, being concerned with page boundaries and a few other cases. We refer to
this part of preparing the PDF file as optimization, discussed in Section 8.3, “Optimization”, page 34. Note the, in
this context, the term optimization is a qpdf term, and the term linearization is a term from the PDF specification. Do
not be confused by the fact that many applications refer to linearization as optimization or web optimization.
When creating linearized PDF files from optimized PDF files, there are really only a few issues that need to be dealt
• Creation of hints tables
• Placing objects in the correct order
• Filling in offsets and byte sizes

8.3. Optimization
In order to perform various operations such as linearization and splitting files into pages, it is necessary to know which
objects are referenced by which pages, page thumbnails, and root and trailer dictionary keys. It is also necessary to
ensure that all page-level attributes appear directly at the page level and are not inherited from parents in the pages tree.
We refer to the process of enforcing these constraints as optimization. As mentioned above, note that some applications
refer to linearization as optimization. Although this optimization was initially motivated by the need to create linearized
files, we are using these terms separately.
PDF file optimization is implemented in the QPDF_optimization.cc source file. That file is richly commented and
serves as the primary reference for the optimization process.
After optimization has been completed, the private member variables obj_user_to_objects and object_to_obj_users in
QPDF have been populated. Any object that has more than one value in the object_to_obj_users table is shared. Any
object that has exactly one value in the object_to_obj_users table is private. To find all the private objects in a page or
a trailer or root dictionary key, one merely has make this determination for each element in the obj_user_to_objects
table for the given page or key.
Note that pages and thumbnails have different object user types, so the above test on a page will not include objects
referenced by the page's thumbnail dictionary and nothing else.



8.4. Writing Linearized Files
We will create files with only primary hint streams. We will never write overflow hint streams. (As of PDF version 1.4,
Acrobat doesn't either, and they are never necessary.) The hint streams contain offset information to objects that point
to where they would be if the hint stream were not present. This means that we have to calculate all object positions
before we can generate and write the hint table. This means that we have to generate the file in two passes. To make
this reliable, QPDFWriter in linearization mode invokes exactly the same code twice to write the file to a pipeline.
In the first pass, the target pipeline is a count pipeline chained to a discard pipeline. The count pipeline simply passes
its data through to the next pipeline in the chain but can return the number of bytes passed through it at any intermediate
point. The discard pipeline is an end of line pipeline that just throws its data away. The hint stream is not written and
dummy values with adequate padding are stored in the first cross reference table, linearization parameter dictionary,
and /Prev key of the first trailer dictionary. All the offset, length, object renumbering information, and anything else
we need for the second pass is stored.
At the end of the first pass, this information is passed to the QPDF class which constructs a compressed hint stream
in a memory buffer and returns it. QPDFWriter uses this information to write a complete hint stream object into a
memory buffer. At this point, the length of the hint stream is known.
In the second pass, the end of the pipeline chain is a regular file instead of a discard pipeline, and we have known values
for all the offsets and lengths that we didn't have in the first pass. We have to adjust offsets that appear after the start of
the hint stream by the length of the hint stream, which is known. Anything that is of variable length is padded, with the
padding code surrounding any writing code that differs in the two passes. This ensures that changes to the way things
are represented never results in offsets that were gathered during the first pass becoming incorrect for the second pass.
Using this strategy, we can write linearized files to a non-seekable output stream with only a single pass to disk or
wherever the output is going.

8.5. Calculating Linearization Data
Once a file is optimized, we have information about which objects access which other objects. We can then process
these tables to decide which part (as described in “Linearized PDF Document Structure” in the PDF specification)
each object is contained within. This tells us the exact order in which objects are written. The QPDFWriter class
asks for this information and enqueues objects for writing in the proper order. It also turns on a check that causes an
exception to be thrown if an object is encountered that has not already been queued. (This could happen only if there
were a bug in the traversal code used to calculate the linearization data.)

8.6. Known Issues with Linearization
There are a handful of known issues with this linearization code. These issues do not appear to impact the behavior of
linearized files which still work as intended: it is possible for a web browser to begin to display them before they are
fully downloaded. In fact, it seems that various other programs that create linearized files have many of these same
issues. These items make reference to terminology used in the linearization appendix of the PDF specification.
• Thread Dictionary information keys appear in part 4 with the rest of Threads instead of in part 9. Objects in part
9 are not grouped together functionally.
• We are not calculating numerators for shared object positions within content streams or interleaving them within
content streams.
• We generate only page offset, shared object, and outline hint tables. It would be relatively easy to add some additional
tables. We gather most of the information needed to create thumbnail hint tables. There are comments in the code
about this.



8.7. Debugging Note
The qpdf --show-linearization command can show the complete contents of linearization hint streams. To look at
the raw data, you can extract the filtered contents of the linearization hint tables using qpdf --show-object=n --filtered-stream-data. Then, to convert this into a bit stream (since linearization tables are bit streams written without
regard to byte boundaries), you can pipe the resulting data through the following perl code:
use bytes;
binmode STDIN;
undef $/;
my $a = ;
my @ch = split(//, $a);
map { printf("%08b", ord($_)) } @ch;
print "\n";


Chapter 9. Object and Cross-Reference
This chapter provides information about the implementation of object stream and cross-reference stream support in

9.1. Object Streams
Object streams can contain any regular object except the following:
• stream objects
• objects with generation > 0
• the encryption dictionary
• objects containing the /Length of another stream
In addition, Adobe reader (at least as of version 8.0.0) appears to not be able to handle having the document catalog
appear in an object stream if the file is encrypted, though this is not specifically disallowed by the specification.
There are additional restrictions for linearized files. See Section 9.3, “Implications for Linearized Files”, page 38for
The PDF specification refers to objects in object streams as “compressed objects” regardless of whether the object
stream is compressed.
The generation number of every object in an object stream must be zero. It is possible to delete and replace an object
in an object stream with a regular object.
The object stream dictionary has the following keys:
• /N: number of objects
• /First: byte offset of first object
• /Extends: indirect reference to stream that this extends
Stream collections are formed with /Extends. They must form a directed acyclic graph. These can be used for
semantic information and are not meaningful to the PDF document's syntactic structure. Although qpdf preserves
stream collections, it never generates them and doesn't make use of this information in any way.
The specification recommends limiting the number of objects in object stream for efficiency in reading and decoding.
Acrobat 6 uses no more than 100 objects per object stream for linearized files and no more 200 objects per stream for
non-linearized files. QPDFWriter, in object stream generation mode, never puts more than 100 objects in an object
Object stream contents consists of N pairs of integers, each of which is the object number and the byte offset of the
object relative to the first object in the stream, followed by the objects themselves, concatenated.

9.2. Cross-Reference Streams
For non-hybrid files, the value following startxref is the byte offset to the xref stream rather than the word xref.


Object and Cross-Reference Streams

For hybrid files (files containing both xref tables and cross-reference streams), the xref table's trailer dictionary contains
the key /XRefStm whose value is the byte offset to a cross-reference stream that supplements the xref table. A
PDF 1.5-compliant application should read the xref table first. Then it should replace any object that it has already
seen with any defined in the xref stream. Then it should follow any /Prev pointer in the original xref table's trailer
dictionary. The specification is not clear about what should be done, if anything, with a /Prev pointer in the xref
stream referenced by an xref table. The QPDF class ignores it, which is probably reasonable since, if this case were
to appear for any sensible PDF file, the previous xref table would probably have a corresponding /XRefStm pointer
of its own. For example, if a hybrid file were appended, the appended section would have its own xref table and /
XRefStm. The appended xref table would point to the previous xref table which would point the /XRefStm, meaning
that the new /XRefStm doesn't have to point to it.
Since xref streams must be read very early, they may not be encrypted, and the may not contain indirect objects for
keys required to read them, which are these:
• /Type: value /XRef
• /Size: value n+1: where n is highest object number (same as /Size in the trailer dictionary)
• /Index (optional): value [n count ...] used to determine which objects' information is stored in this stream.
The default is [0 /Size].
• /Prev: value offset: byte offset of previous xref stream (same as /Prev in the trailer dictionary)
• /W [...]: sizes of each field in the xref table
The other fields in the xref stream, which may be indirect if desired, are the union of those from the xref table's trailer

9.2.1. Cross-Reference Stream Data
The stream data is binary and encoded in big-endian byte order. Entries are concatenated, and each entry has a length
equal to the total of the entries in /W above. Each entry consists of one or more fields, the first of which is the type of
the field. The number of bytes for each field is given by /W above. A 0 in /W indicates that the field is omitted and
has the default value. The default value for the field type is “1”. All other default values are “0”.
PDF 1.5 has three field types:
• 0: for free objects. Format: 0 obj next-generation, same as the free table in a traditional cross-reference table
• 1: regular non-compressed object. Format: 1 offset generation
• 2: for objects in object streams. Format: 2 object-stream-number index, the number of object stream
containing the object and the index within the object stream of the object.
It seems standard to have the first entry in the table be 0 0 0 instead of 0 0 ffff if there are no deleted objects.

9.3. Implications for Linearized Files
For linearized files, the linearization dictionary, document catalog, and page objects may not be contained in object
Objects stored within object streams are given the highest range of object numbers within the main and first-page
cross-reference sections.
It is okay to use cross-reference streams in place of regular xref tables. There are on special considerations.


Object and Cross-Reference Streams

Hint data refers to object streams themselves, not the objects in the streams. Shared object references should also be
made to the object streams. There are no reference in any hint tables to the object numbers of compressed objects
(objects within object streams).
When numbering objects, all shared objects within both the first and second halves of the linearized files must be
numbered consecutively after all normal uncompressed objects in that half.

9.4. Implementation Notes
There are three modes for writing object streams: disable, preserve, and generate. In disable mode, we do not generate
any object streams, and we also generate an xref table rather than xref streams. This can be used to generate PDF
files that are viewable with older readers. In preserve mode, we write object streams such that written object streams
contain the same objects and /Extends relationships as in the original file. This is equal to disable if the file has no
object streams. In generate, we create object streams ourselves by grouping objects that are allowed in object streams
together in sets of no more than 100 objects. We also ensure that the PDF version is at least 1.5 in generate mode, but
we preserve the version header in the other modes. The default is preserve.
We do not support creation of hybrid files. When we write files, even in preserve mode, we will lose any xref tables
and merge any appended sections.


Appendix A. Release Notes
For a detailed list of changes, please see the file ChangeLog in the source distribution.
8.3.0: January 7, 2019
• Command-line Enhancements
• Shell completion: you can now use eval $(qpdf --completion-bash) and eval $(qpdf --completion-zsh) to
enable shell completion for bash and zsh.
• Page numbers (also known as page labels) are now preserved when merging and splitting files with the -pages and --split-pages options.
• Bookmarks are partially preserved when splitting pages with the --split-pages option. Specifically, the outlines dictionary and some supporting metadata are copied into the split files. The result is that all bookmarks
from the original file appear, those that point to pages that are preserved work, and those that point to pages
that are not preserved don't do anything. This is an interim step toward proper support for bookmarks in
splitting and merging operations.
• Page collation: add new option --collate. When specified, the semantics of --pages change from concatenation to collation. See Section 3.5, “Page Selection Options”, page 9 for examples and discussion.
• Generation of information in JSON format, primarily to facilitate use of qpdf from languages other than C
++. Add new options --json, --json-key, and --json-object to generate a JSON representation of the PDF
file. Run qpdf --json-help to get a description of the JSON format. For more information, see Chapter 6,
QPDF JSON, page 22.
• The --generate-appearances flag will cause qpdf to generate appearances for form fields if the PDF file
indicates that form field appearances are out of date. This can happen when PDF forms are filled in by a
program that doesn't know how to regenerate the appearances of the filled-in fields.
• The --flatten-annotations flag can be used to flatten annotations, including form fields. Ordinarily, annotations are drawn separately from the page. Flattening annotations is the process of combining their appearances
into the page's contents. You might want to do this if you are going to rotate or combine pages using a tool
that doesn't understand about annotations. You may also want to use --generate-appearances when using
this flag since annotations for outdated form fields are not flattened as that would cause loss of information.
• The --optimize-images flag tells qpdf to recompresses every image using DCT (JPEG) compression as long
as the image is not already compressed with lossy compression and recompressing the image reduces its
size. The additional options --oi-min-width, --oi-min-height, and --oi-min-area prevent recompression of
images whose width, height, or pixel area (width × height) are below a specified threshold.
• The --show-object option can now be given as --show-object=trailer to show the trailer dictionary.
• Bug Fixes and Enhancements
• QPDF now automatically detects and recovers from dangling references. If a PDF file contained an indirect
reference to a non-existent object, which is valid, when adding a new object to the file, it was possible for the
new object to take the object ID of the dangling reference, thereby causing the dangling reference to point
to the new object. This case is now prevented.
• Fixes to form field setting code: strings are always written in UTF-16 format, and checkboxes and radio
buttons are handled properly with respect to synchronization of values and appearance states.

Release Notes

• The QPDF::checkLinearization() no longer causes the program to crash when it detects problems with linearization data. Instead, it issues a normal warning or error.
• Ordinarily qpdf treats an argument of the form @file to mean that command-line options should be read from
file. Now, if file does not exist but @file does, qpdf will treat @file as a regular option. This makes it possible
to work more easily with PDF files whose names happen to start with the @ character.
• Library Enhancements
• Remove the restriction in most cases that the source QPDF object used in a QPDF::copyForeignObject call
has to stick around until the destination QPDF is written. The exceptional case is when the source stream
gets is data using a QPDFObjectHandle::StreamDataProvider. For a more in-depth discussion, see comments
around copyForeignObject in QPDF.hh.
• Add new method QPDFWriter::getFinalVersion(), which returns the PDF version that will ultimately be
written to the final file. See comments in QPDFWriter.hh for some restrictions on its use.
• Add several methods for transcoding strings to some of the character sets used in PDF files: QUtil::utf8_to_ascii, QUtil::utf8_to_win_ansi, QUtil::utf8_to_mac_roman, and QUtil::utf8_to_utf16. For the single-byte encodings that support only a limited character sets, these methods replace unsupported characters
with a specified substitute.
• Add new methods to QPDFAnnotationObjectHelper and QPDFFormFieldObjectHelper for querying flags and interpretation of different field types. Define constants in qpdf/Constants.h to help with interpretation of flag values.
• Add new methods QPDFAcroFormDocumentHelper::generateAppearancesIfNeeded and QPDFFormFieldObjectHelper::generateAppearance for generating appearance streams. See discussion in QPDFFormFieldObjectHelper.hh for limitations.
• Add two new helper functions for dealing with resource dictionaries: QPDFObjectHandle::getResourceNames() returns a list of all second-level keys, which correspond to the names of resources, and QPDFObjectHandle::mergeResources() merges two resources dictionaries as long as they have non-conflicting keys.
These methods are useful for certain types of objects that resolve resources from multiple places, such as
form fields.
• Add methods QPDFPageDocumentHelper::flattenAnnotations() and QPDFAnnotationObjectHelper::getPageContentForAppearance() for handling low-level details of annotation flattening.
• Add new helper classes: QPDFOutlineDocumentHelper, QPDFOutlineObjectHelper, QPDFPageLabelDocumentHelper, QPDFNameTreeObjectHelper, and QPDFNumberTreeObjectHelper.
• Add method QPDFObjectHandle::getJSON() that returns a JSON representation of the object. Call serialize() on the result to convert it to a string.
• Add a simple JSON serializer. This is not a complete or general-purpose JSON library. It allows assembly
and serialization of JSON structures with some restrictions, which are described in the header file. This is
the serializer used by qpdf's new JSON representation.
• Add new QPDFObjectHandle::Matrix class along with a few convenience methods for dealing with sixelement numerical arrays as matrices.
• Add new method QPDFObjectHandle::wrapInArray, which returns the object itself if it is an array, or an
array containing the object otherwise. This is a common construct in PDF. This method prevents you from
having to explicitly test whether something is a single element or an array.

Release Notes

• Build Improvements
• It is no longer necessary to run autogen.sh to build from a pristine checkout. Automatically generated files
are now committed so that it is possible to build on platforms without autoconf directly from a clean checkout
of the repository. The configure script detects if the files are out of date when it also determines that the
tools are present to regenerate them.
• Pull requests and the master branch are now built automatically in Azure Pipelines [https://dev.azure.com/qpdf/qpdf/_build], which is free for open source projects. The build includes Linux, mac, Windows 32-bit and 64-bit with mingw and MSVC, and an AppImage build. Official qpdf releases are now built
with Azure Pipelines.
• Notes for Packagers
• A new section has been added to the documentation with notes for packagers. Please see Section 2.3, “Notes
for Packagers”, page 3.
• The qpdf detects out-of-date automatically generated files. If your packaging system automatically refreshes libtool or autoconf files, it could cause this check to fail. To avoid this problem, pass --disable-checkautofiles to configure.
• If you would like to have qpdf completion enabled automatically, you can install completion files in the
distribution's default location. You can find sample completion files to install in the completions directory.
8.2.1: August 18, 2018
• Command-line Enhancements
• Add --keep-files-open=[yn] to override default determination of whether to keep files open when merging.
Please see the discussion of --keep-files-open in Section 3.3, “Basic Options”, page 4 for additional details.
8.2.0: August 16, 2018
• Command-line Enhancements
• Add --no-warn option to suppress issuing warning messages. If there are any conditions that would have
caused warnings to be issued, the exit status is still 3.
• Bug Fixes and Optimizations
• Performance fix: optimize page merging operation to avoid unnecessary open/close calls on files being
merged. This solves a dramatic slow-down that was observed when merging certain types of files.
• Optimize how memory was used for the TIFF predictor, drastically improving performance and memory
usage for files containing high-resolution images compressed with Flate using the TIFF predictor.
• Bug fix: end of line characters were not properly handled inside strings in some cases.
• Bug fix: using --progress on very small files could cause an infinite loop.
• API enhancements
• Add new class QPDFSystemError, derived from std::runtime_error, which is now thrown by
QUtil::throw_system_error. This enables the triggering errno value to be retrieved.
• Add ClosedFileInputSource::stayOpen method, enabling a ClosedFileInputSource to stay open during
manually indicated periods of high activity, thus reducing the overhead of frequent open/close operations.

Release Notes

• Build Changes
• For the mingw builds, change the name of the DLL import library from libqpdf.a to libqpdf.dll.a to more
accurately reflect that it is an import library rather than a static library. This potentially clears the way for
supporting a static library in the future, though presently, the qpdf Windows build only builds the DLL and
8.1.0: June 23, 2018
• Usability Improvements
• When splitting files, qpdf detects fonts and images that the document metadata claims are referenced from a
page but are not actually referenced and omits them from the output file. This change can cause a significant
reduction in the size of split PDF files for files created by some software packages. Prior versions of qpdf
would believe the document metadata and sometimes include all the images from all the other pages even
though the pages were no longer present. In the unlikely event that the old behavior should be desired, it can
be enabled by specifying --preserve-unreferenced-resources. For additional details, please see Section 3.7,
“Advanced Transformation Options”, page 11.
• When merging multiple PDF files, qpdf no longer leaves all the files open. This makes it possible to merge
numbers of files that may exceed the operating system's limit for the maximum number of open files.
• The --rotate option's syntax has been extended to make the page range optional. If you specify --rotate=angle without specifying a page range, the rotation will be applied to all pages. This can be especially useful
for adjusting a PDF created from a multi-page document that was scanned upside down.
• When merging multiple files, the --verbose option now prints information about each file as it operates on
that file.
• When the --progress option is specified, qpdf will print a running indicator of its best guess at how far
through the writing process it is. Note that, as with all progress meters, it's an approximation. This option
is implemented in a way that makes it useful for software that uses the qpdf library; see API Enhancements
• Bug Fixes
• Properly decrypt files that use revision 3 of the standard security handler but use 40 bit keys (even though
revision 3 supports 128-bit keys).
• Limit depth of nested data structures to prevent crashes from certain types of malformed (malicious) PDFs.
• In “newline before endstream” mode, insert the required extra newline before the endstream at the end
of object streams. This one case was previously omitted.
• API Enhancements
• The first round of higher level “helper” interfaces has been introduced. These are designed to provide a more
convenient way of interacting with certain document features than using QPDFObjectHandle directly. For
details on helpers, see Section 7.3, “Helper Classes”, page 26. Specific additional interfaces are described
• Add two new document helper classes: QPDFPageDocumentHelper for working with pages, and
QPDFAcroFormDocumentHelper for working with interactive forms. No old methods have been removed, but QPDFPageDocumentHelper is now the preferred way to perform operations on pages rather
than calling the old methods in QPDFObjectHandle and QPDF directly. Comments in the header files
direct you to the new interfaces. Please see the header files and ChangeLog for additional details.

Release Notes

• Add three new object helper class: QPDFPageObjectHelper for pages, QPDFFormFieldObjectHelper
for interactive form fields, and QPDFAnnotationObjectHelper for annotations. All three classes are fairly
sparse at the moment, but they have some useful, basic functionality.
• A new example program examples/pdf-set-form-values.cc has been added that illustrates use of the new
document and object helpers.
• The method QPDFWriter::registerProgressReporter has been added. This method allows you to register a
function that is called by QPDFWriter to update your idea of the percentage it thinks it is through writing its
output. Client programs can use this to implement reasonably accurate progress meters. The qpdf command
line tool uses this to implement its --progress option.
• New methods QPDFObjectHandle::newUnicodeString and QPDFObject::unparseBinary have been added
to allow for more convenient creation of strings that are explicitly encoded using big-endian UTF-16. This
is useful for creating strings that appear outside of content streams, such as labels, form fields, outlines,
document metadata, etc.
• A new class QPDFObjectHandle::Rectangle has been added to ease working with PDF rectangles, which
are just arrays of four numeric values.
8.0.2: March 6, 2018
• When a loop is detected while following cross reference streams or tables, treat this as damage instead of silently
ignoring the previous table. This prevents loss of otherwise recoverable data in some damaged files.
• Properly handle pages with no contents.
8.0.1: March 4, 2018
• Disregard data check errors when uncompressing /FlateDecode streams. This is consistent with most other
PDF readers and allows qpdf to recover data from another class of malformed PDF files.
• On the command line when specifying page ranges, support preceding a page number by “r” to indicate that
it should be counted from the end. For example, the range r3-r1 would indicate the last three pages of a
8.0.0: February 25, 2018
• Packaging and Distribution Changes
• QPDF is now distributed as an AppImage [https://appimage.org/] in addition to all the other ways it is distributed. The AppImage can be found in the download area with the other packages. Thanks to Kurt Pfeifle
and Simon Peter for their contributions.
• Bug Fixes
• QPDFObjectHandle::getUTF8Val now properly treats non-Unicode strings as encoded with PDF Doc Encoding.
• Improvements to handling of objects in PDF files that are not of the expected type. In most cases, qpdf will
be able to warn for such cases rather than fail with an exception. Previous versions of qpdf would sometimes
fail with errors such as “operation for dictionary object attempted on object of wrong type”. This situation
should be mostly or entirely eliminated now.
• Enhancements to the qpdf Command-line Tool. All new options listed here are documented in more detail in
Chapter 3, Running QPDF, page 4.


Release Notes

• The option --linearize-pass1=file has been added for debugging qpdf's linearization code.
• The option --coalesce-contents can be used to combine content streams of a page whose contents are an
array of streams into a single stream.
• API Enhancements. All new API calls are documented in their respective classes' header files. There are no
non-compatible changes to the API.
• Add function qpdf_check_pdf to the C API. This function does basic checking that is a subset of what qpdf
--check performs.
• Major enhancements to the lexical layer of qpdf. For a complete list of enhancements, please refer to the
ChangeLog file. Most of the changes result in improvements to qpdf's ability handle erroneous files. It is
also possible for programs to handle whitespace, comments, and inline images as tokens.
• New API for working with PDF content streams at a lexical level. The new class QPDFObjectHandle::TokenFilter allows the developer to provide token handlers. Token filters can be used with several different
methods in QPDFObjectHandle as well as with a lower-level interface. See comments in QPDFObjectHandle.hh as well as the new examples examples/pdf-filter-tokens.cc and examples/pdf-count-strings.cc for
7.1.1: February 4, 2018
• Bug fix: files whose /ID fields were other than 16 bytes long can now be properly linearized
• A few compile and link issues have been corrected for some platforms.
7.1.0: January 14, 2018
• PDF files contain streams that may be compressed with various compression algorithms which, in some cases,
may be enhanced by various predictor functions. Previously only the PNG up predictor was supported. In this
version, all the PNG predictors as well as the TIFF predictor are supported. This increases the range of files
that qpdf is able to handle.
• QPDF now allows a raw encryption key to be specified in place of a password when opening encrypted files, and
will optionally display the encryption key used by a file. This is a non-standard operation, but it can be useful in
certain situations. Please see the discussion of --password-is-hex-key in Section 3.3, “Basic Options”, page 4
or the comments around QPDF::setPasswordIsHexKey in QPDF.hh for additional details.
• Bug fix: numbers ending with a trailing decimal point are now properly recognized as numbers.
• Bug fix: when building qpdf from source on some platforms (especially MacOS), the build could get confused
by older versions of qpdf installed on the system. This has been corrected.
7.0.0: September 15, 2017
• Packaging and Distribution Changes
• QPDF's primary license is now version 2.0 of the Apache License [http://www.apache.org/licenses/LICENSE-2.0] rather than version 2.0 of the Artistic License. You may still, at your option, consider qpdf to
be licensed with version 2.0 of the Artistic license.
• QPDF no longer has a dependency on the PCRE (Perl-Compatible Regular Expression) library. QPDF now
has an added dependency on the JPEG library.
• Bug Fixes


Release Notes

• This release contains many bug fixes for various infinite loops, memory leaks, and other memory errors that
could be encountered with specially crafted or otherwise erroneous PDF files.
• New Features
• QPDF now supports reading and writing streams encoded with JPEG or RunLength encoding. Library API enhancements and command-line options have been added to control this behavior. See command-line options --compress-streams and --decode-level and methods QPDFWriter::setCompressStreams
and QPDFWriter::setDecodeLevel.
• QPDF is much better at recovering from broken files. In most cases, qpdf will skip invalid objects and will
preserve broken stream data by not attempting to filter broken streams. QPDF is now able to recover or at
least not crash on dozens of broken test files I have received over the past few years.
• Page rotation is now supported and accessible from both the library and the command line.
• QPDFWriter supports writing files in a way that preserves PCLm compliance in support of driverless printing. This is very specialized and is only useful to applications that already know how to create PCLm files.
• Enhancements to the qpdf Command-line Tool. All new options listed here are documented in more detail in
Chapter 3, Running QPDF, page 4.
• Command-line arguments can now be read from files or standard input using @file or @- syntax. Please
see Section 3.1, “Basic Invocation”, page 4.
• --rotate: request page rotation
• --newline-before-endstream: ensure that a newline appears before every endstream keyword in the file;
used to prevent qpdf from breaking PDF/A compliance on already compliant files.
• --preserve-unreferenced: preserve unreferenced objects in the input PDF
• --split-pages: break output into chunks with fixed numbers of pages
• --verbose: print the name of each output file that is created
• --compress-streams and --decode-level replace --stream-data for improving granularity of controlling
compression and decompression of stream data. The --stream-data option will remain available.
• When running qpdf --check with other options, checks are always run first. This enables qpdf to perform
its full recovery logic before outputting other information. This can be especially useful when manually
recovering broken files, looking at qpdf's regenerated cross reference table, or other similar operations.
• Process --pages earlier so that other options like --show-pages or --split-pages can operate on the file after
page splitting/merging has occurred.
• API Changes. All new API calls are documented in their respective classes' header files.
• QPDFObjectHandle::rotatePage: apply rotation to a page object
• QPDFWriter::setNewlineBeforeEndstream: force newline to appear before endstream
• QPDFWriter::setPreserveUnreferencedObjects: preserve unreferenced objects that appear in the input PDF.
The default behavior is to discard them.


Release Notes

• New Pipeline types Pl_RunLength and Pl_DCT are available for developers who wish to produce or
consume RunLength or DCT stream data directly. The examples/pdf-create.cc example illustrates their use.
• QPDFWriter::setCompressStreams and QPDFWriter::setDecodeLevel methods control handling of different types of stream compression.
• Add new C API functions qpdf_set_compress_streams, qpdf_set_decode_level, qpdf_set_preserve_unreferenced_objects, and qpdf_set_newline_before_endstream corresponding to the new QPDFWriter methods.
6.0.0: November 10, 2015
• Implement --deterministic-id command-line option and QPDFWriter::setDeterministicID as well as C API
function qpdf_set_deterministic_ID for generating a deterministic ID for non-encrypted files. When this option
is selected, the ID of the file depends on the contents of the output file, and not on transient items such as the
timestamp or output file name.
• Make qpdf more tolerant of files whose xref table entries are not the correct length.
5.1.3: May 24, 2015
• Bug fix: fix-qdf was not properly handling files that contained object streams with more than 255 objects in
• Bug fix: qpdf was not properly initializing Microsoft's secure crypto provider on fresh Windows installations
that had not had any keys created yet.
• Fix a few errors found by Gynvael Coldwind and Mateusz Jurczyk of the Google Security Team. Please see
the ChangeLog for details.
• Properly handle pages that have no contents at all. There were many cases in which qpdf handled this fine, but
a few methods blindly obtained page contents with handling the possibility that there were no contents.
• Make qpdf more robust for a few more kinds of problems that may occur in invalid PDF files.
5.1.2: June 7, 2014
• Bug fix: linearizing files could create a corrupted output file under extremely unlikely file size circumstances.
See ChangeLog for details. The odds of getting hit by this are very low, though one person did.
• Bug fix: qpdf would fail to write files that had streams with decode parameters referencing other streams.
• New example program: pdf-split-pages: efficiently split PDF files into individual pages. The example program
does this more efficiently than using qpdf --pages to do it.
• Packaging fix: Visual C++ binaries did not support Windows XP. This has been rectified by updating the
compilers used to generate the release binaries.
5.1.1: January 14, 2014
• Performance fix: copying foreign objects could be very slow with certain types of files. This was most likely
to be visible during page splitting and was due to traversing the same objects multiple times in some cases.
5.1.0: December 17, 2013
• Added runtime option (QUtil::setRandomDataProvider) to supply your own random data provider. You can
use this if you want to avoid using the OS-provided secure random number generation facility or stdlib's less
secure version. See comments in include/qpdf/QUtil.hh for details.


Release Notes

• Fixed image comparison tests to not create 12-bit-per-pixel images since some versions of tiffcmp have bugs
in comparing them in some cases. This increases the disk space required by the image comparison tests, which
are off by default anyway.
• Introduce a number of small fixes for compilation on the latest clang in MacOS and the latest Visual C++ in
• Be able to handle broken files that end the xref table header with a space instead of a newline.
5.0.1: October 18, 2013
• Thanks to a detailed review by Florian Weimer and the Red Hat Product Security Team, this release includes a
number of non-user-visible security hardening changes. Please see the ChangeLog file in the source distribution
for the complete list.
• When available, operating system-specific secure random number generation is used for generating initialization vectors and other random values used during encryption or file creation. For the Windows build, this results
in an added dependency on Microsoft's cryptography API. To disable the OS-specific cryptography and use the
old version, pass the --enable-insecure-random option to ./configure.
• The qpdf command-line tool now issues a warning when -accessibility=n is specified for newer encryption
versions stating that the option is ignored. qpdf, per the spec, has always ignored this flag, but it previously
did so silently. This warning is issued only by the command-line tool, not by the library. The library's handling
of this flag is unchanged.
5.0.0: July 10, 2013
• Bug fix: previous versions of qpdf would lose objects with generation != 0 when generating object streams.
Fixing this required changes to the public API.
• Removed methods from public API that were only supposed to be called by QPDFWriter and couldn't realistically be called anywhere else. See ChangeLog for details.
• New QPDFObjGen class added to represent an object ID/generation pair. QPDFObjectHandle::getObjGen() is
now preferred over QPDFObjectHandle::getObjectID() and QPDFObjectHandle::getGeneration() as it makes
it less likely for people to accidentally write code that ignores the generation number. See QPDF.hh and
QPDFObjectHandle.hh for additional notes.
• Add --show-npages command-line option to the qpdf command to show the number of pages in a file.
• Allow omission of the page range within --pages for the qpdf command. When omitted, the page range is
implicitly taken to be all the pages in the file.
• Various enhancements were made to support different types of broken files or broken readers. Details can be
found in ChangeLog.
4.1.0: April 14, 2013
• Note to people including qpdf in distributions: the .la files generated by libtool are now installed by qpdf's make
install target. Before, they were not installed. This means that if your distribution does not want to include .la
files, you must remove them as part of your packaging process.
• Major enhancement: API enhancements have been made to support parsing of content streams. This enhancement includes the following changes:


Release Notes

• QPDFObjectHandle::parseContentStream method parses objects in a content stream and calls handlers in a
callback class. The example examples/pdf-parse-content.cc illustrates how this may be used.
• QPDFObjectHandle can now represent operators and inline images, object types that may only appear
in content streams.
• Method QPDFObjectHandle::getTypeCode() returns an enumerated type value representing the underlying
object type. Method QPDFObjectHandle::getTypeName() returns a text string describing the name of the
type of a QPDFObjectHandle object. These methods can be used for more efficient parsing and debugging/diagnostic messages.
• qpdf --check now parses all pages' content streams in addition to doing other checks. While there are still many
types of errors that cannot be detected, syntactic errors in content streams will now be reported.
• Minor compilation enhancements have been made to facilitate easier for support for a broader range of compilers
and compiler versions.
• Warning flags have been moved into a separate variable in autoconf.mk
• The configure flag --enable-werror work for Microsoft compilers
• All MSVC CRT security warnings have been resolved.
• All C-style casts in C++ Code have been replaced by C++ casts, and many casts that had been included to
suppress higher warning levels for some compilers have been removed, primarily for clarity. Places where
integer type coercion occurs have been scrutinized. A new casting policy has been documented in the manual.
This is of concern mainly to people porting qpdf to new platforms or compilers. It is not visible to programmers writing code that uses the library
• Some internal limits have been removed in code that converts numbers to strings. This is largely invisible
to users, but it does trigger a bug in some older versions of mingw-w64's C++ library. See README-windows.md in the source distribution if you think this may affect you. The copy of the DLL distributed with
qpdf's binary distribution is not affected by this problem.
• The RPM spec file previously included with qpdf has been removed. This is because virtually all Linux distributions include qpdf now that it is a dependency of CUPS filters.
• A few bug fixes are included:
• Overridden compressed objects are properly handled. Before, there were certain constructs that could cause
qpdf to see old versions of some objects. The most usual manifestation of this was loss of filled in form
values for certain files.
• Installation no longer uses GNU/Linux-specific versions of some commands, so make install works on
Solaris with native tools.
• The 64-bit mingw Windows binary package no longer includes a 32-bit DLL.
4.0.1: January 17, 2013
• Fix detection of binary attachments in test suite to avoid false test failures on some platforms.
• Add clarifying comment in QPDF.hh to methods that return the user password explaining that it is no longer
possible with newer encryption formats to recover the user password knowing the owner password. In earlier
encryption formats, the user password was encrypted in the file using the owner password. In newer encryption
formats, a separate encryption key is used on the file, and that key is independently encrypted using both the
user password and the owner password.


Release Notes

4.0.0: December 31, 2012
• Major enhancement: support has been added for newer encryption schemes supported by version X of Adobe
Acrobat. This includes use of 127-character passwords, 256-bit encryption keys, and the encryption scheme
specified in ISO 32000-2, the PDF 2.0 specification. This scheme can be chosen from the command line by
specifying use of 256-bit keys. qpdf also supports the deprecated encryption method used by Acrobat IX. This
encryption style has known security weaknesses and should not be used in practice. However, such files exist “in
the wild,” so support for this scheme is still useful. New methods QPDFWriter::setR6EncryptionParameters
(for the PDF 2.0 scheme) and QPDFWriter::setR5EncryptionParameters (for the deprecated scheme) have
been added to enable these new encryption schemes. Corresponding functions have been added to the C API
as well.
• Full support for Adobe extension levels in PDF version information. Starting with PDF version 1.7, corresponding to ISO 32000, Adobe adds new functionality by increasing the extension level rather than increasing
the version. This support includes addition of the QPDF::getExtensionLevel method for retrieving the document's extension level, addition of versions of QPDFWriter::setMinimumPDFVersion and QPDFWriter::forcePDFVersion that accept an extension level, and extended syntax for specifying forced and minimum versions
on the command line as described in Section 3.7, “Advanced Transformation Options”, page 11. Corresponding
functions have been added to the C API as well.
• Minor fixes to prevent qpdf from referencing objects in the file that are not referenced in the file's overall
structure. Most files don't have any such objects, but some files have contain unreferenced objects with errors,
so these fixes prevent qpdf from needlessly rejecting or complaining about such objects.
• Add new generalized methods for reading and writing files from/to programmer-defined sources. The
method QPDF::processInputSource allows the programmer to use any input source for the input file, and
QPDFWriter::setOutputPipeline allows the programmer to write the output file through any pipeline. These
methods would make it possible to perform any number of specialized operations, such as accessing external
storage systems, creating bindings for qpdf in other programming languages that have their own I/O systems,
• Add new method QPDF::getEncryptionKey for retrieving the underlying encryption key used in the file.
• This release includes a small handful of non-compatible API changes. While effort is made to avoid such
changes, all the non-compatible API changes in this version were to parts of the API that would likely never
be used outside the library itself. In all cases, the altered methods or structures were parts of the QPDF that
were public to enable them to be called from either QPDFWriter or were part of validation code that was overzealous in reporting problems in parts of the file that would not ordinarily be referenced. In no case did any of
the removed methods do anything worse that falsely report error conditions in files that were broken in ways
that didn't matter. The following public parts of the QPDF class were changed in a non-compatible way:
• Updated nested QPDF::EncryptionData class to add fields needed by the newer encryption formats, member variables changed to private so that future changes will not require breaking backward compatibility.
• Added additional parameters to compute_data_key, which is used by QPDFWriter to compute the encryption key used to encrypt a specific object.
• Removed the method flattenScalarReferences. This method was previously used prior to writing a new PDF
file, but it has the undesired side effect of causing qpdf to read objects in the file that were not referenced.
Some otherwise files have unreferenced objects with errors in them, so this could cause qpdf to reject files
that would be accepted by virtually all other PDF readers. In fact, qpdf relied on only a very small part of
what flattenScalarReferences did, so only this part has been preserved, and it is now done directly inside
• Removed the method decodeStreams. This method was used by the --check option of the qpdf command-line
tool to force all streams in the file to be decoded, but it also suffered from the problem of opening otherwise


Release Notes

unreferenced streams and thus could report false positive. The --check option now causes qpdf to go through
all the motions of writing a new file based on the original one, so it will always reference and check exactly
those parts of a file that any ordinary viewer would check.
• Removed the method trimTrailerForWrite. This method was used by QPDFWriter to modify the original
QPDF object by removing fields from the trailer dictionary that wouldn't apply to the newly written file.
This functionality, though generally harmless, was a poor implementation and has been replaced by having
QPDFWriter filter these out when copying the trailer rather than modifying the original QPDF object. (Note
that qpdf never modifies the original file itself.)
• Allow the PDF header to appear anywhere in the first 1024 bytes of the file. This is consistent with what other
readers do.
• Fix the pkg-config files to list zlib and pcre in Requires.private to better support static linking using pkg-config.
3.0.2: September 6, 2012
• Bug fix: QPDFWriter::setOutputMemory did not work when not used with QPDFWriter::setStaticID, which
made it pretty much useless. This has been fixed.
• New API call QPDFWriter::setExtraHeaderText inserts additional text near the header of the PDF file. The
intended use case is to insert comments that may be consumed by a downstream application, though other use
cases may exist.
3.0.1: August 11, 2012
• Version 3.0.0 included addition of files for pkg-config, but this was not mentioned in the release notes. The
release notes for 3.0.0 were updated to mention this.
• Bug fix: if an object stream ended with a scalar object not followed by space, qpdf would incorrectly report that
it encountered a premature EOF. This bug has been in qpdf since version 2.0.
3.0.0: August 2, 2012
• Acknowledgment: I would like to express gratitude for the contributions of Tobias Hoffmann toward the release
of qpdf version 3.0. He is responsible for most of the implementation and design of the new API for manipulating
pages, and contributed code and ideas for many of the improvements made in version 3.0. Without his work,
this release would certainly not have happened as soon as it did, if at all.
• Non-compatible API change: The version of QPDFObjectHandle::replaceStreamData that uses a StreamDataProvider no longer requires (or accepts) a length parameter. See Appendix C, Upgrading to 3.0, page 58
for an explanation. While care is taken to avoid non-compatible API changes in general, an exception was made
this time because the new interface offers an opportunity to significantly simplify calling code.
• Support has been added for large files. The test suite verifies support for files larger than 4 gigabytes, and
manual testing has verified support for files larger than 10 gigabytes. Large file support is available for both
32-bit and 64-bit platforms as long as the compiler and underlying platforms support it.
• Support for page selection (splitting and merging PDF files) has been added to the qpdf command-line tool.
See Section 3.5, “Page Selection Options”, page 9.
• Options have been added to the qpdf command-line tool for copying encryption parameters from another file.
See Section 3.3, “Basic Options”, page 4.
• New methods have been added to the QPDF object for adding and removing pages. See Section 7.8, “Adding
and Removing Pages”, page 30.


Release Notes

• New methods have been added to the QPDF object for copying objects from other PDF files. See Section 7.10,
“Copying Objects From Other PDF Files”, page 31
• A new method QPDFObjectHandle::parse has been added for constructing QPDFObjectHandle objects
from a string description.
• Methods have been added to QPDFWriter to allow writing to an already open stdio FILE* addition to writing
to standard output or a named file. Methods have been added to QPDF to be able to process a file from an
already open stdio FILE*. This makes it possible to read and write PDF from secure temporary files that have
been unlinked prior to being fully read or written.
• The QPDF::emptyPDF can be used to allow creation of PDF files from scratch. The example examples/pdfcreate.cc illustrates how it can be used.
• Several methods to take PointerHolder can now also accept std::string arguments.
• Many new convenience methods have been added to the library, most in QPDFObjectHandle. See ChangeLog for a full list.
• When building on a platform that supports ELF shared libraries (such as Linux), symbol versions are enabled
by default. They can be disabled by passing --disable-ld-version-script to ./configure.
• The file libqpdf.pc is now installed to support pkg-config.
• Image comparison tests are off by default now since they are not needed to verify a correct build or port of
qpdf. They are needed only when changing the actual PDF output generated by qpdf. You should enable them
if you are making deep changes to qpdf itself. See README.md for details.
• Large file tests are off by default but can be turned on with ./configure or by setting an environment variable
before running the test suite. See README.md for details.
• When qpdf's test suite fails, failures are not printed to the terminal anymore by default. Instead, find them in
build/qtest.log. For packagers who are building with an autobuilder, you can add the --enable-show-failedtest-output option to ./configure to restore the old behavior.
2.3.1: December 28, 2011
• Fix thread-safety problem resulting from non-thread-safe use of the PCRE library.
• Made a few minor documentation fixes.
• Add workaround for a bug that appears in some versions of ghostscript to the test suite
• Fix minor build issue for Visual C++ 2010.
2.3.0: August 11, 2011
• Bug fix: when preserving existing encryption on encrypted files with cleartext metadata, older qpdf versions
would generate password-protected files with no valid password. This operation now works. This bug only affected files created by copying existing encryption parameters; explicit encryption with specification of cleartext metadata worked before and continues to work.
• Enhance QPDFWriter with a new constructor that allows you to delay the specification of the output file.
When using this constructor, you may now call QPDFWriter::setOutputFilename to specify the output file,
or you may use QPDFWriter::setOutputMemory to cause QPDFWriter to write the resulting PDF file to a
memory buffer. You may then use QPDFWriter::getBuffer to retrieve the memory buffer.


Release Notes

• Add new API call QPDF::replaceObject for replacing objects by object ID
• Add new API call QPDF::swapObjects for swapping two objects by object ID
• Add QPDFObjectHandle::getDictAsMap and QPDFObjectHandle::getArrayAsVector to allow retrieval of
dictionary objects as maps and array objects as vectors.
• Add functions qpdf_get_info_key and qpdf_set_info_key to the C API for manipulating string fields of the
document's /Info dictionary.
• Add functions qpdf_init_write_memory, qpdf_get_buffer_length, and qpdf_get_buffer to the C API for writing
PDF files to a memory buffer instead of a file.
2.2.4: June 25, 2011
• Fix installation and compilation issues; no functionality changes.
2.2.3: April 30, 2011
• Handle some damaged streams with incorrect characters following the stream keyword.
• Improve handling of inline images when normalizing content streams.
• Enhance error recovery to properly handle files that use object 0 as a regular object, which is specifically
disallowed by the spec.
2.2.2: October 4, 2010
• Add new function qpdf_read_memory to the C API to call QPDF::processMemoryFile. This was an omission
in qpdf 2.2.1.
2.2.1: October 1, 2010
• Add new method QPDF::setOutputStreams to replace std::cout and std::cerr with other streams for generation
of diagnostic messages and error messages. This can be useful for GUIs or other applications that want to
capture any output generated by the library to present to the user in some other way. Note that QPDF does
not write to std::cout (or the specified output stream) except where explicitly mentioned in QPDF.hh, and
that the only use of the error stream is for warnings. Note also that output of warnings is suppressed when
setSuppressWarnings(true) is called.
• Add new method QPDF::processMemoryFile for operating on PDF files that are loaded into memory rather
than in a file on disk.
• Give a warning but otherwise ignore empty PDF objects by treating them as null. Empty object are not permitted
by the PDF specification but have been known to appear in some actual PDF files.
• Handle inline image filter abbreviations when the appear as stream filter abbreviations. The PDF specification
does not allow use of stream filter abbreviations in this way, but Adobe Reader and some other PDF readers
accept them since they sometimes appear incorrectly in actual PDF files.
• Implement miscellaneous enhancements to PointerHolder and Buffer to support other changes.
2.2.0: August 14, 2010
• Add new methods to QPDFObjectHandle (newStream and replaceStreamData for creating new streams and
replacing stream data. This makes it possible to perform a wide range of operations that were not previously


Release Notes

• Add new helper method in QPDFObjectHandle (addPageContents) for appending or prepending new content
streams to a page. This method makes it possible to manipulate content streams without having to be concerned
whether a page's contents are a single stream or an array of streams.
• Add new method in QPDFObjectHandle: replaceOrRemoveKey, which replaces a dictionary key with a
given value unless the value is null, in which case it removes the key instead.
• Add new method in QPDFObjectHandle: getRawStreamData, which returns the raw (unfiltered) stream data
into a buffer. This complements the getStreamData method, which returns the filtered (uncompressed) stream
data and can only be used when the stream's data is filterable.
• Provide two new examples: pdf-double-page-size and pdf-invert-images that illustrate the newly added interfaces.
• Fix a memory leak that would cause loss of a few bytes for every object involved in a cycle of object references.
Thanks to Jian Ma for calling my attention to the leak.
2.1.5: April 25, 2010
• Remove restriction of file identifier strings to 16 bytes. This unnecessary restriction was preventing qpdf from
being able to encrypt or decrypt files with identifier strings that were not exactly 16 bytes long. The specification
imposes no such restriction.
2.1.4: April 18, 2010
• Apply the same padding calculation fix from version 2.1.2 to the main cross reference stream as well.
• Since qpdf --check only performs limited checks, clarify the output to make it clear that there still may be
errors that qpdf can't check. This should make it less surprising to people when another PDF reader is unable
to read a file that qpdf thinks is okay.
2.1.3: March 27, 2010
• Fix bug that could cause a failure when rewriting PDF files that contain object streams with unreferenced objects
that in turn reference indirect scalars.
• Don't complain about (invalid) AES streams that aren't a multiple of 16 bytes. Instead, pad them before decrypting.
2.1.2: January 24, 2010
• Fix bug in padding around first half cross reference stream in linearized files. The bug could cause an assertion
failure when linearizing certain unlucky files.
2.1.1: December 14, 2009
• No changes in functionality; insert missing include in an internal library header file to support gcc 4.4, and
update test suite to ignore broken Adobe Reader installations.
2.1: October 30, 2009
• This is the first version of qpdf to include Windows support. On Windows, it is possible to build a DLL. Additionally, a partial C-language API has been introduced, which makes it possible to call qpdf functions from nonC++ environments. I am very grateful to Žarko Gajic (http://zarko-gajic.iz.hr/) for tirelessly testing numerous
pre-release versions of this DLL and providing many excellent suggestions on improving the interface.
For programming to the C interface, please see the header file qpdf/qpdf-c.h and the example examples/pdflinearize.c.


Release Notes

• Žarko Gajic has written a Delphi wrapper for qpdf, which can be downloaded from qpdf's download side.
Žarko's Delphi wrapper is released with the same licensing terms as qpdf itself and comes with this disclaimer:
“Delphi wrapper unit qpdf.pas created by Žarko Gajic (http://zarko-gajic.iz.hr/). Use at your own risk and for
whatever purpose you want. No support is provided. Sample code is provided.”
• Support has been added for AES encryption and crypt filters. Although qpdf does not presently support files
that use PKI-based encryption, with the addition of AES and crypt filters, qpdf is now be able to open most
encrypted files created with newer versions of Acrobat or other PDF creation software. Note that I have not
been able to get very many files encrypted in this way, so it's possible there could still be some cases that qpdf
can't handle. Please report them if you find them.
• Many error messages have been improved to include more information in hopes of making qpdf a more useful
tool for PDF experts to use in manually recovering damaged PDF files.
• Attempt to avoid compressing metadata streams if possible. This is consistent with other PDF creation applications.
• Provide new command-line options for AES encrypt, cleartext metadata, and setting the minimum and forced
PDF versions of output files.
• Add additional methods to the QPDF object for querying the document's permissions. Although qpdf does
not enforce these permissions, it does make them available so that applications that use qpdf can enforce permissions.
• The --check option to qpdf has been extended to include some additional information.
• There have been a handful of non-compatible API changes. For details, see Appendix B, Upgrading from 2.0
to 2.1, page 57.
2.0.6: May 3, 2009
• Do not attempt to uncompress streams that have decode parameters we don't recognize. Earlier versions of qpdf
would have rejected files with such streams.
2.0.5: March 10, 2009
• Improve error handling in the LZW decoder, and fix a small error introduced in the previous version with regard
to handling full tables. The LZW decoder has been more strongly verified in this release.
2.0.4: February 21, 2009
• Include proper support for LZW streams encoded without the “early code change” flag. Special thanks to Atom
Smasher who reported the problem and provided an input file compressed in this way, which I did not previously
• Implement some improvements to file recovery logic.
2.0.3: February 15, 2009
• Compile cleanly with gcc 4.4.
• Handle strings encoded as UTF-16BE properly.
2.0.2: June 30, 2008
• Update test suite to work properly with a non-bash /bin/sh and with Perl 5.10. No changes were made to the
actual qpdf source code itself for this release.


Release Notes

2.0.1: May 6, 2008
• No changes in functionality or interface. This release includes fixes to the source code so that qpdf compiles
properly and passes its test suite on a broader range of platforms. See ChangeLog in the source distribution
for details.
2.0: April 29, 2008
• First public release.


Appendix B. Upgrading from 2.0 to 2.1
Although, as a general rule, we like to avoid introducing source-level incompatibilities in qpdf's interface, there were a
few non-compatible changes made in this version. A considerable amount of source code that uses qpdf will probably
compile without any changes, but in some cases, you may have to update your code. The changes are enumerated here.
There are also some new interfaces; for those, please refer to the header files.
• QPDF's exception handling mechanism now uses std::logic_error for internal errors and std::runtime_error
for runtime errors in favor of the now removed QEXC classes used in previous versions. The QEXC exception
classes predated the addition of the  header file to the C++ standard library. Most of the exceptions
thrown by the qpdf library itself are still of type QPDFExc which is now derived from std::runtime_error.
Programs that caught an instance of std::exception and displayed it by calling the what() method will not need
to be changed.
• The QPDFExc class now internally represents various fields of the error condition and provides interfaces for
querying them. Among the fields is a numeric error code that can help applications act differently on (a small number
of) different error conditions. See QPDFExc.hh for details.
• Warnings can be retrieved from qpdf as instances of QPDFExc instead of strings.
• The nested QPDF::EncryptionData class's constructor takes an additional argument. This class is primarily intended to be used by QPDFWriter. There's not really anything useful an end-user application could do with it. It
probably shouldn't really be part of the public interface to begin with. Likewise, some of the methods for computing
internal encryption dictionary parameters have changed to support /R=4 encryption.
• The method QPDF::getUserPassword has been removed since it didn't do what people would think it did. There
are now two new methods: QPDF::getPaddedUserPassword and QPDF::getTrimmedUserPassword. The first one
does what the old QPDF::getUserPassword method used to do, which is to return the password with possible binary
padding as specified by the PDF specification. The second one returns a human-readable password string.
• The enumerated types that used to be nested in QPDFWriter have moved to top-level enumerated types and are
now defined in the file qpdf/Constants.h. This enables them to be shared by both the C and C++ interfaces.


Appendix C. Upgrading to 3.0
For the most part, the API for qpdf version 3.0 is backward compatible with versions 2.1 and later. There are two
• The method QPDFObjectHandle::replaceStreamData that uses a StreamDataProvider to provide the stream
data no longer takes a length parameter. While it would have been easy enough to keep the parameter for backward
compatibility, in this case, the parameter was removed since this provides the user an opportunity to simplify the
calling code. This method was introduced in version 2.2. At the time, the length parameter was required in order
to ensure that calls to the stream data provider returned the same length for a specific stream every time they were
invoked. In particular, the linearization code depends on this. Instead, qpdf 3.0 and newer check for that constraint
explicitly. The first time the stream data provider is called for a specific stream, the actual length is saved, and
subsequent calls are required to return the same number of bytes. This means the calling code no longer has to
compute the length in advance, which can be a significant simplification. If your code fails to compile because of
the extra argument and you don't want to make other changes to your code, just omit the argument.
• Many methods take long long instead of other integer types. Most if not all existing code should compile fine
with this change since such parameters had always previously been smaller types. This change was required to
support files larger than two gigabytes in size.


Appendix D. Upgrading to 4.0
While version 4.0 includes a few non-compatible API changes, it is very unlikely that anyone's code would have
used any of those parts of the API since they generally required information that would only be available inside the
library. In the unlikely event that you should run into trouble, please see the ChangeLog. See also Appendix A, Release
Notes, page 40 for a complete list of the non-compatible API changes made in this version.



Source Exif Data:
File Type                       : PDF
File Type Extension             : pdf
MIME Type                       : application/pdf
Linearized                      : Yes
Create Date                     : 2019:01:08 01:17:23Z
Creator                         : Apache FOP Version 2.1
Format                          : application/pdf
Language                        : en
Date                            : 2019:01:08 01:17:23Z
Producer                        : Apache FOP Version 2.1
PDF Version                     : 1.4
Creator Tool                    : Apache FOP Version 2.1
Metadata Date                   : 2019:01:08 01:17:23Z
Page Count                      : 64
Profile CMM Type                : Little CMS
Profile Version                 : 2.3.0
Profile Class                   : Display Device Profile
Color Space Data                : RGB
Profile Connection Space        : XYZ
Profile Date Time               : 2004:08:13 12:18:06
Profile File Signature          : acsp
Primary Platform                : Apple Computer Inc.
CMM Flags                       : Not Embedded, Independent
Device Manufacturer             : Little CMS
Device Model                    : 
Device Attributes               : Reflective, Glossy, Positive, Color
Rendering Intent                : Perceptual
Connection Space Illuminant     : 0.9642 1 0.82491
Profile Creator                 : Little CMS
Profile ID                      : 0
Device Mfg Desc                 : lcms generated
Profile Description             : sRGB
Device Model Desc               : sRGB
Media White Point               : 0.95015 1 1.08826
Red Matrix Column               : 0.43585 0.22238 0.01392
Blue Matrix Column              : 0.14302 0.06059 0.71384
Green Matrix Column             : 0.38533 0.71704 0.09714
Red Tone Reproduction Curve     : (Binary data 2060 bytes, use -b option to extract)
Green Tone Reproduction Curve   : (Binary data 2060 bytes, use -b option to extract)
Blue Tone Reproduction Curve    : (Binary data 2060 bytes, use -b option to extract)
Chromaticity Channels           : 3
Chromaticity Colorant           : Unknown (0)
Chromaticity Channel 1          : 0.64 0.33
Chromaticity Channel 2          : 0.3 0.60001
Chromaticity Channel 3          : 0.14999 0.06
Profile Copyright               : no copyright, use freely
EXIF Metadata provided by EXIF.tools

Navigation menu