This is a very complex part of file distribution and I hope we have solved that nicely and easily:
For every PRODUCT / FILE, we introduced new fields for the calls of external programs. If you take a look at the eBooks, we sell, you will see a difference to the other files on sale.
1st: for the eBooks is a user input required. This can be plugged in the shopping process.
2nd: to download the eBooks a backend communication to mobipocket is required and we wrote a nice PHP program, which does that (by the way, our Mobipocket PHP toolkit is now distributed by them ;-)
So, handling DRM for your files requires some external programs and we can plug that into the shopping process easily.
Cheers,
Puzzler