I wonder how we can reason property when signing pdf-document. And i cannot see that signed certificate became validated. If sign with same certificate ie. Nitro application signing stamp will be validated and seeing all properties filled properly.
And also we cannot see how we set security that only printing and test copy is allowed.
Since REST APIs are a wrapper around Native APIs, implementation/availability of these features in REST APIs would not take much time. I have logged a request in our internal tracking software for the implementation of these features and will update you here once a new version with requested APIs is available.
Please note we have implemented your requested features. Please try following APIs for signature verification and document privileges. Hopefully it will help you to accomplish the task.