Open Source C PDF Software

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

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.

Sumatra PDF is a free PDF, eBook (ePub, Mobi), XPS, DjVu, CHM, Comic Book (CBZ and CBR) viewer for Windows. Sumatra PDF is powerful, small, portable and starts up very fast. Simplicity of the user interface has a high priority. Portable version is a single executable, can be run from USB drive and doesn't write to registry. For best results use the latest release available as that's what I use and test with. If things don't compile, first make sure you're using the latest version of Visual Studio. To compile you need Visual Studio 2019 16.6 or later. Free Community edition works.

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.