/etc/messages, but according to Google they were not relevant. Than I found a post describing the same behaviour, noting that starting KPDF as root worked. I checked it, same with me.
When starting KPDF from the commandline, a warning is shown:
kpdf: WARNING: Unknown mimetype 'application/x-kdeuser1'.
This hints at the solution: Adobe Reader installation obviously messed up mime types, going to Konqueror -> Settings -> Configure Konqueror -> File Associations -> Known Types -> applications and deleting user
x-kdeuser1(I also had
) solved the problem.