Our team has further looked into this issue and I just wanted to share the update with you. As you’re trying to set privileges on an already signed PDF that’s why you’re having problem. In fact, both signing and setting privileges methods are concerned with encryption, and you can’t encrypt an already signed PDF.
Moreover, we also need your input to proceed further on this issue. Can you please elaborate your requirement in current scenario? What exactly are you trying to achieve by signing and setting privileges at the same time? If you elaborate your requirement or goal in a bit more detail, I’m sure our team would be in a better position to help you out.
We’re sorry for the inconvenience and appreciate your cooperation.