Q:
Is it possible using PDFNet SDK to secure pdf document with password and set expiration date of this password? Or maybe it is possible to do something with pdf document to force it to be unreadable after specified date? If it’s possible please give any code samples in c#.
A:
The following forum post may be of some interest to you:
https://groups.google.com/d/msg/pdfnet-sdk/dJpyhULyYUA/0ozIje6-m5kJ
https://groups.google.com/d/msg/pdfnet-sdk/8N0DSeIpjRg/RjJG454oEfsJ
In short, while there is no password expiration mechanism built into the PDF format, you could customize PDFNet viewer code to enforce document expiration. This is kind of DRM is easiest with WebViewer (http://www.pdftron.com/webviewer/index.html, http://www.pdftron.com/webviewer/showcase/).