I use PDFs. I also use a textpad to keep track of my experience, HP, PP, bleed, etc. For games where I need to do a lot of bookkeeping as a character, one game in particular, I use a collection of files rather than paper documents to keep track of what I do. For exemple, one document detailing all the books I put my hands on (the character is a loremaster), one to keep track of time, economic investments and items for trade (he is also an alchemist), etc. Depends on how complex the game is... 90% of the games, I mostly use a computer for the PDFs and keeping track of combat stats. But I might have a file for summoning tables, if I play a summoner, and so on.