QPDF

QPDF is a command-line tool and C++ library for performing structural transformations on PDF files. It allows inspection, manipulation, and optimization of the internal structure of PDF documents without altering their main visual content.

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• Linearization (web optimization). This function reorganizes the internal structure of the PDF file to allow progressive rendering in web browsers. It places the cross-reference table and the objects needed for the first page at the beginning of the file. This process allows pages to be displayed before the entire file is downloaded.
• Encryption and decryption. This function applies or removes password-based security on PDF files according to PDF encryption standards. It supports standard 40-bit and 128-bit encryption algorithms (RC4 and AES). It allows configuring specific user permissions, such as prohibiting printing or document modification.
• Object compression and decompression. This function converts individual PDF objects into compressed object streams to reduce file size. It can also perform the reverse operation, decompressing object streams to obtain a PDF with each object separately accessible. This transformation does not affect page content streams.
• Plain text editing mode. This function converts a binary PDF file into a structured ASCII representation that can be edited with a text editor. It preserves the object and reference structure, allowing controlled modifications of metadata, bookmarks, or the document structure, which can then be converted back to a valid PDF.
• Merging PDF documents. This function combines pages from multiple PDF files into a single document. It copies the page objects and necessary resources from the source documents to the destination document. It maintains the integrity of shared resources and avoids conflicts between identical object names from different files.
• Splitting PDF documents. This function extracts specific page ranges from a PDF document to create new independent files. It creates new PDF documents containing only the objects referenced by the selected pages, including fonts, images, and other resources necessary for their correct display.
• Structure inspection and reporting. This function analyzes the internal structure of the PDF file and generates detailed plain text reports. It shows the object hierarchy, the catalog dictionary, the page list, embedded fonts, XMP metadata, and the cross-reference table. It identifies unreferenced objects or structural errors.
• Repairing damaged files. This function attempts to reconstruct the structure of corrupt or incomplete PDF files. It rebuilds the cross-reference table from the objects found in the file stream. It corrects incorrect object offsets and generates a new valid PDF file with as much recoverable data as possible.
• Component extraction. This function allows extracting specific elements from a PDF file, such as embedded images, fonts, page content streams, or metadata. Extracted elements are saved to separate files in their native format. For images, they are converted to standard formats like JPEG or PNG when possible.
• Page rotation and reordering. This function modifies the order of pages within the document or applies rotations to specific pages. It updates the page dictionary and inherited rotations without reprocessing the graphical content. This operation is fast as it only affects page layout metadata.
• Metadata manipulation. This function allows adding, modifying, or removing document metadata, including the Info dictionary information and XMP metadata. It updates fields like title, author, subject, and keywords. It maintains consistency between traditional (Info) metadata and modern XMP metadata when both are present.
• Removal of password restrictions. This function removes the user password restrictions from a PDF file when the correct user password is provided. The resulting file retains all its functionalities but no longer requires a password to open. It does not remove the owner password that restricts permissions.
• PDF creation from scratch. This library function allows programmatically generating valid PDF files by providing all the objects and their structure. The library handles correct syntax, cross-reference table generation, offset calculation, and final file formatting, while the developer controls the content.
• Standards compliance verification. This function analyzes the PDF file and identifies features that do not meet specific PDF/A, PDF/UA, or other standard specifications. It generates a detailed report of the issues found, although it does not perform automatic corrections to achieve compliance.

The development of QPDF began in 2001 by Jay Berkenbilt. The project arose from the need for a tool that could reliably perform structural transformations on PDF files, without relying on commercial libraries. The first public version was released in 2003 under the Apache License version 2.0. The program is primarily written in C++, with some supporting components in shell scripts and Python for building and testing.

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