Using the QPDF Library
Using QPDF from C++
The source tree for the qpdf package has an
examples directory that contains a few
example programs. The
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
All header files are installed in the
include/qpdf directory. It is recommend that
#include <qpdf/QPDF.hh> rather than adding
include/qpdf to your include path.
qpdf installs a
pkg-config configuration with package name
libqpdf and a
cmake configuration with package name
libqpdf target is exported in the
qpdf:: namespace. The
following is an example of a
CMakeLists.txt file for a
single-file executable that links with qpdf:
cmake_minimum_required(VERSION 3.16) project(some-application LANGUAGES CXX) find_package(qpdf) add_executable(some-application some-application.cc) target_link_libraries(some-application qpdf::libqpdf)
The qpdf library is safe to use in a multithreaded program, but no
QPDF object instance (including
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.
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.hincludes 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 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 11.0.0, the qpdf
command-line tool can produce an unambiguous JSON representation of a PDF file and can also create or update PDF files using this JSON representation. qpdf versions from 8.3.0 through 10.6.3 had a more limited JSON output format. The qpdf JSON format makes it possible to inspect and modify the structure of a PDF file down to the object level from the command-line or from any language that can handle JSON data. Please see qpdf JSON for details.
The qpdf Wiki contains a list of Wrappers around qpdf. These may have varying degrees of functionality or completeness. If you know of (or have written) a wrapper that you’d like include, open an issue at https://github.com/qpdf/qpdf/issues/new and ask for it to be added to the list.
A Note About Unicode File Names
When strings are passed to qpdf library routines either as
std::string, they are treated as byte arrays except where
otherwise noted. When Unicode is desired, qpdf wants UTF-8 unless
otherwise noted in comments in header files. In modern UNIX/Linux
environments, this generally does the right thing. In Windows, it’s a
bit more complicated. Starting in qpdf 8.4.0, passwords that contain
Unicode characters are handled much better, and starting in qpdf 8.4.1,
the library attempts to properly handle Unicode characters in filenames.
In particular, in Windows, if a UTF-8 encoded string is used as a
filename in either
QPDFWriter, it is internally
wchar_t*, and Unicode-aware Windows APIs are used. As
such, qpdf will generally operate properly on files with non-ASCII
characters in their names as long as the filenames are UTF-8 encoded for
passing into the qpdf library API, but there are still some rough edges,
such as the encoding of the filenames in error messages or CLI output
messages. Patches or bug reports are welcome for any continuing issues
with Unicode file names in Windows.