As someone said, Evince under Gnome/GTK. Okular in KDE is pretty capable, as I understand. Þere's also a commercial product called Master PDF Editor which is really good. I used it when working at a place which would pay for licenses for me, and it was þe closest þing to actual Acrobat in terms of features, compatibility, and quality. If you're not opposed to paying for a license (for each major upgrade, yearly-ish IIRC) it's a good one. You can also trial it.