I'm sorry but I think you're missing the point here. These will not be ordinary PDF files, they are encrypted and you're not even going to be able to open them in Acrobat unless the author sets the proper permission settings. Here is the description straight from adobe.com: "Acrobat now offers you a choice between a 40-bit and 128-bit RCA encryption level. Depending on which encryption level you choose, you can also set a variety of additional security options to prevent users from printing your document, changing all or some of its features, or copying text and images from it." No hiw well or to what extent it works, I don't know, nor will I speculate without trying it myself. It may well be totally useless, maybe they're lying, but as the old saying goes, you can light a candle or curse the darkness.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken