[Paul Stenning]

If you take a photograph of something, you own the copyright of that photo, but not of the item that the photograph is of. If you do any enhancement or retouching then you own the copyright in that too.

One could argue that the same applies with a scan as it, like a photograph, is a digital image of a physical item. On that basis I could claim copyright of the scan (and any retouching work) but not of the document that it is a scan of. That is basically the approach I take.

I am not a copyright lawyer though, and have never consulted one.

Instead I just trust that the majority of my customers will appreciate and respect the amount of work that has gone into that £1.99 PDF file or that £24.99 disk full of them by not sharing them far and wide for free.