PDF Password Protector Software

@maz1207 (221)
Malaysia
November 6, 2011 11:18pm CST
Hello, i have an ebook and thinking of selling it but i need a PDF password protector software that only my buyers will get. After they pay, i will give the password to them. I would want that if they ask for a refund, they won't get access to my ebook too as maybe the password change automatically or whatever. Can someone please suggest pdf password protector that can do this? Thanks.
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