How do you ensure people can not copy your materials and steal your ideas.

Question

We have a number of training manuals and we just print them for our participants.  A number of participants every year ask for e-copies. Its a great idea but how do I ensure they can not copy the materials and re-purpose it for their own use. In worse case scenerio they could copy huge chunks of the manuals and become competitors.
The searchable feature is one reason sited by clients for e-copies.  This kind of shuts down the scan -OCR approach. To make it searchable would be a sizable task.
Some approach to limit easy copying;
bi-column writing columns
Waterwarks
encrypted passwords - however this still may allow it to be passed around to wider audiences.
I feel like I'm asking futile question in the modern e-era, how do i lock down my materials allow for ease of use and distribution and yet ensure our IP is not distributed beyond the intended audience.

Answer 1

Staying on paper provides only the perception of "protection".
It is trivial to prep a hardcopy source, scan the paper, OCR and have it all in PDF.
While Acrobat's OCR will do an adequate job one can step up to something more robust if desired.
Once PDFs with OCR output are in hand it is, again, trivial to export the textual content.
Going to TXT, RTF, DOC or DOCX  lets one clean up, edit, etc.
Go digital. Apply appropriate copyright information to metadata and elsewhere.
Monitor your field of endeavor. At the end of the day it really is a limit field of play with limited players in a very big world.
Should you come across the baddies have the lawyers tree 'em eh.
If you've a end-user friendly, usable product you will get more "end-users". 
Be well...