In the version of the XPS Viewer that’s included with .NET Framework 3.0, you can verify an XPS document's authenticity with adigital signature and protect a document's contents with permissions.
A digital signature enables you to both verify that your XPS document hasn’t been changed since you signed it and to verify another XPS document’s publisher so you can make sure it comes from a trusted source before you open it.
You can also create permission restrictions for your XPS document so that no one can view, copy, print, or digitally sign your document without your permission. You can set time restrictions on permissions, allow as many or as few permissions as you want to other users, and allow different users to have different levels of access.
In the XPS Essentials Pack, which is the standalone version of the XPS Viewer, you can view, copy, or print XPS documents, but you cannot digitally sign or set new permissions for a document.