Why are screen caps in .PDF ? How to change ?

[Peter Nacken]

I wondered about that one long time already ... When I do screen caps, they
turn out as .pdf files ... Which are either linked to adobe acrobat (on my
iBook) or Preview (on my iMac)  ... Now .. I just tried Graphic Converter to
do a batch conversion .. Ta daaa . GC does not open PDF ...

Is there a way to change the output format of screen caps ? If not, an easy
way to do a batch conversion ? I was really surprised GC would not do that

Thanks

P