Externally verified digital signatures

We developed a system that uses the PDFNet product. This has proved
successful so far. Our client has asked us to extend the
functionality that we provide to include the application of an
externally verified digital certificate to the PDF’s we produce with
PDFNet.

My questions are as follows

1) Does PDFNet support the application of an externally verified
digital certificate
2) Are there any restriction/specification to the type of certificates
which can be applied to the PDF using PDFNet (if any),
3) What is the best approach to doing this.
4) How do you associate a digital signature field in pdfnet with a
digital ID
5) Can pdfnet work with an Adobe Certified Document Services (CDS)
provider

Many thanks in advance for any helphelp