Okay, I take back what I commented earlier. Just talked to one of the senior guys in my shop and he said it is possible to lock it down hard. What you can do is convert the pdf to an image/flash/whatever and wrap it in an iFrame. Then, you create another image with 100% transparency and lay it over top the iFrame (not in it) and set it to have a higher Z-value than the iFrame.
What this will do is that if they right click on the 'image' to save it, they will be saving the transparent image instead. And since the image 'overrides' the iFrame, any attempt to use print screen should be shielded by the image, and they should only be able to snapshot the image that doesn't actually exist.
That leaves only one or two ways to get at the file...which requires digging straight into the source code to find the image file inside the iFrame. Still not totally secure, but protected from your average user.
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