Split and merge PDFs using PDFSAM (PDF Split and Merge), a free and lightweight tool. Available at http://www.pdfsam.org.
I’ve been using Foxit PDF Reader (think “free full version of Adobe”) for years now. Though they recently changed it so that it has a bit of (in my opinion) bloat (e.g. unnecessary features, crowded toolbars), and I’m still getting used to the new interface, it’s still probably the best option for academics who want a program that lets them not just read but highlight, use comment bubbles, and write on PDFs. (It doesn’t mention that in the list of features, but, yes, it does all that).