If you’re like me, you spend significant amounts of time digesting PDFs. Papers, articles, documentation and the like. On OSX, the default Preview application does a good job of displaying files, but several things from the dead-tree experience are lacking:

• I like to, if I’m really diving into a paper, mark it up: highlighter, underline, questions in the margin and scribbles galore.

• Like a printout, how would I convey notes and such to someone else? If I’ve printed it and scribbled, I can just give it to them, but if I use another program to take notes (e.g. Voodoo pad) then it’s a pain to share.

A while ago I found (via Cool OSX Apps) the solution, a free program called Skim. Here’s an example screenshot, where I’ve used most all of the annotation tools on a single page to show the possibilities:

(Click for fullsize)

As you can see, you have highlighter, box, yellow post-it, side notes, freehand doodles, elliptical mark, and lines. I’m pretty sure there’s even more I haven’t found yet.

What’s more, any annotations are saved as part of the file, (see below, I was wrong on this) so they can be shared, saved and reopened later when you’ve forgotten that key insight. S’wonderful.

Highly recommended. Consider setting it to be the default program for PDF files as I have, and spend 30 minutes learning how to use it. For me, this was one of the last real reasons to print stuff out, now vanquished. Bravo.

Update 3/28: Commenter JRF points out that I hadn’t read the Skim FAQ, which explains that the annotations are stored in extended attributes and not the file itself. This makes them more fragile and hard to send via email, svn or the like. Skim is still useful, but read the FAQ if you want to share the results.