Adobe Reader lets you read the pdf: that's about it. Foxit Reader provides numerous tools for editing, such as highlighting and annotating the text. It's much faster than Adobe Reader, too. If you're looking for a free pdf viewer/editor, Foxit is your program.
Though last time I checked, the Linux version still needed A LOT of work; if you use Linux, you can just run the Windows version through Wine instead. It works great.