WWF.de have come up with an idea to help us decide which documents don't need to waste paper, the save as WWF option. Forget tired old PDF's, most of these PDF's don't have to be printed at all, why not alert the recipient from the get-go by making your PDF impossible to print? Just download the WWF software, and you'll have the unprintable pdf option WWF available in your adobe.
Only available for Mac osX right now, but a windows version is coming soon. Brilliant! Save as WWF, save a tree! The paperless office might finally arrive.