WWF file format: it's like a PDF that's impossible to print

Have you ever received a PDF in your email, only to find yourself weeping moments later after accidentally printing 349 copies and murdering six or seven endangered trees in the Panamanian rain forest? It's more serious of a problem than you may realize. In order to solve spontaneous bouts of Accident Print Syndrome, the World Wide Fund For Nature has created the WWF file format. We'll let the entity itself explain:

The WWF format is a PDF that cannot be printed out. It's a simple way to avoid unnecessary printing. So here's your chance to save trees and help the environment. Decide for yourself which documents don't need printing out – then simply save them as WWF.

For now, it's only readable on a Mac, which means that WWF files also cannot be printed from a PC. We're envisioning a world of college professors using these to prevent printable study guides, but so as long as hackers also exist in that same universe, those who prefer their documents on paper -- and HP's ink department -- will probably figure out their own road to nirvana. Must to the dismay of Ma Earth, of course.