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.
Reporting engine library written in C. Create one XML file and generate PDF, HTML, TXT, and CSV reports based on queries. Has support for MySQL, PostgreSQL, ODBC. Bindings for PHP, Java, Python.