Open Source C PDF Software

QPDF is a C++ library and set of programs that inspect and manipulate the structure of PDF files. It can encrypt and linearize files, expose the internals of a PDF file, and do many other operations useful to end users and PDF developers.

pdfcrack is a command line, password recovery tool for PDF-files.

Vanilla.PDF is a modern, high-performance, open-source C++17 SDK designed for creating, editing, signing, and analyzing PDF documents across multiple platforms. It requires no external runtime dependencies, making it lightweight and ideal for embedding into desktop applications, servers, or automation pipelines. The SDK offers full cross-platform support including Windows, Linux, macOS, and Android, with builds available for major compilers and architectures. Vanilla.PDF supports advanced PDF features such as adding CMS (PKCS#7) digital signatures, modifying content streams and metadata, and working with encryption and permissions based on standard PDF security models. It includes tools for parsing PDF internals like cross-reference tables and objects, providing fine-grained document analysis capabilities. The project is unit-tested with continuous integration pipelines, supporting sanitizers for enhanced code quality and stability.

Cross-platform command-line tool for creation of PDF documents from scans/photos of pages in JPEG (.jpg) format and the lightest weight ANSI C library to put multiple JPEG files into one PDF file. You can add handwritten comments to PDF scans (over original images) with xournal: http://xournal.sourceforge.net/ It supports graphics tablets and saves comments to PDFs as vector data.