I'm trying to sell a PDF file. I'm going to burn it and sell it on a CD locally. My fear is that one of the buyers will upload it online and make it available for free to the others. I was wondering if there's a way to make that uploaded file unable to open when someone downloads it. I'd like that copy I sold to be restricted to that one customer. I'm assuming the only way to do that is to restrict it to one computer, since it's impossible to restrict it to a person per se. So then how do I restrict it to one computer?
Even if I give a different password for each copy, the person who uploaded it could still post the password for that copy. So is there a free way to restrict it to one computer, workable on both PC or mac?
PS.These customers are not very tech savvy(but maybe enough to know how to upload a file and password). And the information in the PDF is somewhat time-perishable, meaning that maybe after a year it will be worthless. So I don't really need methods that are too aggressive/hard.
Send out the CD with a password that is equal to their personal/social security number and/or their e-mail address. This might make them not want to provide the credentials to the WWW. I'm now presuming they're dumb enough to think protected PDF:s are secure, and that they're concerned about privacy.
Provide the PDF inside of a custom format reader that has no export abilities and embed the PDF in your custom format within the executable. Use an obfuscator to further obstruct the decompiling process.
Provide an external physical device that has a unique algorithm on it, responding differently to various inputs (common for internet bank security solutions). Require internet access to the material in an SWF or Java Applet using the techniques in "n00b Hacker Security", where you use the user credentials and the physical device's response to confirm that the algorithm matches that which you've sent to the particular user.
This is out of my league. And even if it wasn't, any suggestions here can be hacked too.