I’ve worked with the specs in different formats – MS Word, MS Excel, PDF, TXT, scanned images and so on. For PDF specs I use Foxit Reader – I love it (and I don’t like Adobe Acrobat). I it allows me to make comments, draw primitive figures and so on.
Often the specs contain a lot of unnecessary information – list of authors, notes, history of changes, “how to read this spec” section and other junk which bothers you and distracts from your work – I hate scrolling all of these pages to the right one 🙂 If the spec in MS Word or TXT format, you can simply delete these blah-blah pages. But you are not so flexible with PDF. I use this: I simply “print” essential pages with my PDF printer (one comes with the Foxit Reader):