On a Mac, I like Skim.app or Preview. Skim is less aggressive about saving changes right away. I crop the pages, then read a two-page spread in full screen.

On a Mac, I like Skim.app or Preview. Skim is less aggressive about saving changes right away. I crop the pages, then read a two-page spread in full screen. You can also split the view if you want to refer to a non-adjacent page, though unfortunately only horizontal splits seem to work. Everything's legible enough on a non-retina 21" imac.