THERE IS NO SUCH THING AS 100% SECURITY FOR DIGITAL PRODUCTS!
Being a stubborn, and probably naive, so-and-so I always harboured the belief that *somewhere* there was a security solution that could never be cracked...
I was wrong, dead wrong.
I won't mention his name, or his company, but i've had a response today from someone who runs a well-known company whose sole endeavor is to secure digital products from unauthorised viewing.
He went in to some detail with me about how my claim was true, and how his solution had indeed been cracked. His company's security solutions (for .pdf e-book security) start at around $5-6,000 per year. He also explained that company's who are more expensive than that have also had their security compromised.
I feel for the guy, I really really do!... it felt like he was spilling his heart out to me, to be honest. Anyway, the upshot of this is: NO solution is 100% secure. If you are going to "secure" your products for sale then I guess the best advice is to try and do the least obtrusive solution possible, for the customers you are selling to.
So if, e.g. you are doing some .exe download, and your customers start complaining, then it may be an idea to go back to .pdf.