How can i create certified pdf with c#?
A certified PDF is basically a PDF that has been digitally signed using a certificate that is trusted by the Adobe Root Certificate. This service is called Adobe Certified Document Services. When your document is signed it displays a blue ribbon at the top and verifies that the document is from you and it hasn't been tampered with.
You can get the certificate from a participant of the service, we use one called GlobalSign
Once you have the certificate you need to get a device to actually sign the documents, this can be a USB stick that you plug into your PC or a PCI HSM card that sits in a server for high volume signing.
Once you have this in place your PDF's will display the blue ribbon
In our system we used Morphon Tom to actually sign the PDFs, it's a webservice that you simply send a PDF to and it returns it signed using your certificate.
Hope this gets you started!