In my experience links and form fields are the two above you encounter most often in the real world. The problem with forms though is that you potentially open up scripting, for better or worse. I mean you're already in Javascript, so you could handle it a lot easier than Preview on MacOS could, but it is of course worrisome that you'll be running code from an arbitrary PDF…

I wish I was still working at Apple and had my suite of nasty PDF's to test with. Some were just huge files (like a catalog for McMaster-Carr or wherever), another (a version of The Bible?) had an odd text layout across the columns on each page (for testing text selection), maybe one file was a huge single-page PDF street-map of a city (with lots and lots of rendering code and arbitrary text runs all across the map, etc.).