If you just need to open PDF documents in Kubuntu you can do so using Okular, if you are in the Xubuntu you can run Xpdf and if you are with the Unity desktop enviroment you can use Evince.
You probably already have them all installed in your computer, and I dont think you need to be running a KDE session to run Okular, nor a Xfce session to run Xpdf. So what I am saying is that you can probably run any of them from any session, give them a test and report the results here.
Good luck to you!
Last edited by TroN-0074; 05-03-2012 at 05:54 PM.