How to make annotations on .PDF files like on Okular, but without using Okular? What .PDF viewer should I use?

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http://askubuntu.com – So guys, I'm answering some question from a school test (saved in .pdf) and I would like to do it like I did once on Okular, using a cursor-pen to mark the alternatives. Like on this screenshot from Okular official website. As you can see, he traced the title with a cursor-pen, this is what I want to do. And I'm using Ubuntu 11.10 not Kubuntu. (HowTos)