Skim | PDF/E-book Reader (Mac)
October 6 2009, 2:19pm
"Your Mac's default PDF reader, Preview, does let you add sticky notes to pages, but Skim throws highlighting and circling into the mix, giving you more note-taking options. In addition, you can see all of your notes in outline form and jump to their locations, making this a great tool for marking up PDFs. Your notes are saved in the PDF but will only be read by Skim, meaning you can get a clean version back at any time by just opening the file with Preview. Skim is free, requires Mac OS X."
