ok
to answer my own question
think I found the answer in this post from Tumnus:
'Filename extensions (e.g. .pdf) are associated with a filetype using /home/QtPalmtop/etc/mime.types
Those mime.types are then associated with applications via the .desktop files under the subdirectories in /home/QtPalmtop/apps
To ensure qpdf has the association with PDFs, you'll have to remove the PDF mime type from the opera.desktop file and put a new mime type line in the qpdf.desktop file with the PDF mime type.'
-only problem -I checked all the desktop files in /home/QtPalmtop/apps and they were all blank?
keef