Prot-On is an application that allows you to protect, manage and track the use of all kinds of files that are shared on the Internet, by e-mail or through a cloud service.
Easy To Use:
Prot-On is very easy to use. Just download the application and create an account.
With the application installed you can protect your documents and manage access permissions through a management panel accessible at any time and from any device.
The service is free for all users, without time or use limits. For advanced functionality Prot-On offers versions for professionals and corporate users.
Best Part Is:
Prot-On does not store copies of the documents that you protect; they only store the keys and the permission rights.
And other good thing is just with one click you can change who can access the protected document (or any of its copies) and when.
More at: http://en.prot-on.com/tryIt.html