Comment SendSide - https://www.sendside.com/ (Score 1) 237
There is no way to prevent someone from doing something like taking a photo of all the pages on a screen and sending them to someone.
However, a product like Sendside will let you track everyone who receives, opens, and forwards a message that you send.
If you are really paranoid you can use encryption on the document and make all recipients provide their own encryption keys.