What to use to annotate PDF (Highlight/Underline) [duplicate]
You can use Xournal. Works on my 64bit system.
The KDE default Okular (http://en.wikipedia.org/wiki/Okular) supports highlighting, underlining and so on.
Try http://www.mendeley.com/. They have a nice client with a reader that can annotate, and it's great for organizing your PDFs as well.