Well golly gee - when you photocopy the thing, invisible "VOID" words appear all over it. These are not even visible on the original document.
Nor are they on a color copy, meaning anyone who wants to copy their documents is going to spend at least 50 cents doing it, instead of about 8.
Or you use Photoshop, which anybody making a fake one is going to do anyway.
And nowhere in anything they sent me is anything marked "do not copy". I fact, I don't think I have ever seen an original document publicly posted anywhere I've been. They have all been copies, usually with the address information obliterated out.