SelectPdf for .NET - Advanced Pdf Security Settings and Digital Signatures - C# / ASP.NET Sample This sample shows how to modify security settings of an existing PDF document using SelectPdf, how to set a password to be able to view or modify the document (password: 'test1' and 'test2') and also specifies user permissions for the pdf document (if the user can print, copy content, fill forms, modify, etc). Here is our initial test pdf document: Test file The pdf document encryption can be done using either RC4 or AES algorithm, using 40 bit, 128 bit or 256 bit encryption keys. The sample also show how to sign an existing PDF document using a PFX certificate. Sample PFX certificate file: Certificate IMPORTANT: Please note that the certificate used is a self signed certificate generated for testing purposes only. The signature will appear as not valid in a pdf viewer. Using a valid certificate will result in a valid digital signature.