[Exmortis]

There is no way for them to do anything about user entered material being shared. Hell they probably don't even remember we exist.

However as a person who detests stealing, if I was this position to share an adventure or rule book I entered, I would request in an email an attestation that the person does legitimately own the material (PDF or book).

For myself that would be enough. I have no idea on the legalities of such matters and it probably various by country a great deal. However I hate draconian laws as much as I hate thieves, one usually follows due actions of the other. Most people are honest, and most who love a hobby want to support it, and buying the materials is the one true way to do so. So if they say they own, unless I have reason to believe otherwise, I would share the material.