apache/pdfbox

OpenPDF is an open-source Java library for creating, editing, rendering, and encrypting PDF documents, as well as generating PDFs from HTML. It is licensed under the LGPL and MPL.

iText for Java represents the next level of SDKs for developers that want to take advantage of the benefits PDF can bring. Equipped with a better document engine, high and low-level programming capabilities and the ability to create, edit and enhance PDF documents, iText can be a boon to nearly every workflow.

qpdf: A content-preserving PDF document transformer

borb is a library for reading, creating and manipulating PDF files in python.

A Python library for reading and writing PDF, powered by QPDF

PHP PDF Library (TCPDF)

A pure-python PDF library capable of splitting, merging, cropping, and transforming the pages of PDF files

PDF4QT is an open-source PDF toolkit for Windows and Linux, combining powerful desktop applications, command-line tools and a modern MIT-licensed C++/Qt PDF engine.