how can i secure a pdf as a digital download product? i know that one can use adobe's built in pdf security to prevent copy and paste and printing but my understanding is that those can be defeated by Apple viewers for example. even if those are not defeated it would be simple for someone to just share the pdf with all of their friends or post it on a site where anyone could download it for free. is the only way to truly secure a pdf as a digital product to have the viewer code on a server? if that is the answer does such a product exist?