[KUbuntu Gutsy] How to avoid acrobat as the default for PDFs?

After having installed Acrobat Reader 8.1.1 under KUbuntu Gutsy, I'm no longer able to use kpdf as the default PDF viewer.
I've tried to oped a PDF with "Open with...", choosing the KPDF program and setting it as the default choice.
Nonetheless everytime I click on a PDF file I still get Acrobat Reader (which I'm willing to use only under some circumstances).
How can I avoid acrobat as the default PDF viewer?

Thanks a lot.