Goodreader is an excellent PDF repository and reader if you have a large library (I’m a TTRPG gamer) although you can get by with iBooks. I find Google Drive a

Goodreader is an excellent PDF repository and reader if you have a large library (I’m a TTRPG gamer) although you can get by with iBooks. I find Google Drive and Google Docs indispensable, but Notability is also excellent. The built in notes app is surprisingly capable though, so you might as well check it out.