I'm looking for software that would allow someone, when creating a document (before they send it) to specify the other users who are allowed to see it. The ideal solution would allow users to add people who are outside of their organization as well. However, if that person forwarded it to yet another person, they would not be able to view the document unless they are given permission by the original creator.
I have seen solutions that come close, but they either do not allow for sending to external recipients, only secure the documents upon sending, but not before while they are "at rest," or they require the purchase and use of a special appliance, which I would also prefer to avoid.
Thanks for your help! Any ideas are appreciated.