Problem solved by removing ~/.trinity/share/applnk/kpdf_part.desktop
which had contained:
[Desktop Entry]
Exec=
MimeType=
Name=KPDF
Terminal=false
Type=Application
X-TDE-InitialPreference=17
Google seems to suggest that applnk was a pre KDE 3.2 menu structure.
That's a long time ago and I don't know how kpdf's applnk got into
my ~/.trinity. There are no other applnk files.
Thanks to everybody who provided helpful clues.
--Mike