KPDF has been developed into Okular which supports a system for bookmarks, comments, for forms and multimedia contents and a multicolumn view. KPDF is however still available.
The core of the program consists of a library, which abstract modules for every single format. The functionality and the appropriate graphical user interface can be integrated in other programs.
As with all PDF readers it can have difficulty rendering or printing documents that other PDF readers may cope with. Now that both Adobe Reader and KPDF are depreciated for good reason in OpenSuse, Evince may help solve an issue.
...and many more.