GNU PDF

The GNU PDF project is developing a free, high-quality and fully functional set of libraries and programs that implement the PDF file format and associated technologies to the coming ISO standard, ISO 32000.

Why? Isn't PDF support "fine"?

According to José Marchesi, quoted by Bruce Byfield missing or incomplete features in Free Software PDF implementations include:

"interactive features (forms, annotations), the management of embedded contents (sounds and movies), execution of JavaScript to perform forms validation, 3-D artwork, accessibility, Web capturing, [and] management of document collections."

Contributions page for GNU PDF: https://www.fsf.org/donate/directed-donations/gnupdf.html