@Nuder_Try
What I'd probably do:
View the PDF, then grab the page with SGrab. Save as e.g. PNG.
Scale the resulting picture to the desired size (I normally use homecooked scripts and NetPBM, but there are loads of tools that can do that).
Using any old icon (of the correct type, e.g. project or tool) renamed as <your file>.info, call up icon information (assuming you use RaWBInfo). Use the menu to load your picture as icon image, then save the icon.
Note: Haven't tested my description, but something like that ...
Best regards,
Niels