Securing documents .. cloud? other?

Hi there..

I am wondering if anyone can suggest a product or service for secure document exchange.  We have a small number of highly sensitive CAD drawings that we would like some engineers to work on.  We want to allow them to view and potentially modify these documents, but strictly control (or at least audit) their ability to re-save, print or otherwise copy the CAD content.  Ideally we'd like to prevent them from taking screen captures as well.  Ideally I am looking for a web-hosted option for something like this, but something strictly applied at a Windows server/share could be appropriate too.  I would also be interested in any similar services that could deal with PDF (or similar) document formats as well.

Suggestions are most welcome!