Yea that makes some sense, especially if your cost is very low.
You've no doubt weighed things out much more than I ever will so there are probably reasons I wouldn't be aware of. But at first light I'm not sure what use your manual would be to folks other than those who have purchased one of your boards, so the proprietary cautions aren't connecting for me. Again, I know nothing and if you didn't have some good reasons I'm sure you wouldn't have needed to send the manual that way.

Having said that, IF there isn't significant material to protect, then having at least parts of the manual available for download might be good for marketing! Maybe that would be yet another thing to spend your time on - editing an abridged version of the manual to whet the appetite for potential customers. Browsing a nice manual is almost close to being able to touch and feel the board.

OK my work here is done. I've delegated homework to others like a good supervisor and now I can go take a nap.