Are you using gnome, and talking about the icon which appears in nautilus (the file browser)?
If so, I think the default behaviour is to render a small preview of the first page of the document for the icon view. Do you just want to prevent this?
You can prevent it using gconf-editor (press alt-f2 and enter "gconf-editor" in the dialog). Then search for pdf and in the settings, change "enable" to false:
- /desktop/gnome/thumbnailers/application@pdf
- /desktop/gnome/thumbnailers/application@x-bzpdf
- /desktop/gnome/thumbnailers/application@x-gzpdf
I am not sure how to change the default icon for a PDF after the preview is disabled though, but I am not a gnome user - I'm sure someone out there knows.
