One interesting thing to note about pdf libraries is there seems to be a general trend towards A/GPL licenses, presumably because working with PDFs are tedious

One interesting thing to note about pdf libraries is there seems to be a general trend towards A/GPL licenses, presumably because working with PDFs are tedious but still the standard for conveying data intended for human consumption/archival. The commercial licensing for some of these is a little hairy, too. I've seen rev share clauses which is, uh, hilarious. Depending on what you're doing, check your licenses!