The guys at The Pragmatic Programmers (http://www.pragmaticprogrammer.com/) 
do this. You might want to get in touch with them.

Josef Lowder wrote:
> .
> How can one modify a pdf file that was created from a postscript 
> source with 'ps2pdf' so that it can be offered as a compressed 
> "ebook" but with its contents protected so the text cannot be 
> de-compiled or exported (as with 'pdftotext' or something similar)? 
> 
> Also, any suggestions on the best way to offer an 'ebook' for 
> immediate download on the 'net (either with or without charging 
> a fee for it)? 
> 
> I have had some requests for a couple of books I have published 
> to be made available as ebooks. 
> 
> 

-- 
-Eric 'shubes'
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