[video=youtube;_ywfefiwWFY]http://www.youtube.com/watch?v=_ywfefiwWFY[/video]
In case you don't want to watch the video I will explain:
First, this works for projects with Microsoft Word or Microsoft Powerpoint, as it corrupts the file. You don't have to make the project then corrupt it, just splash some random letters and then corrupt it.
Or, if you want, there are online sites that will do it.
For example this:
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