An ability to be able to tell using c# if 1) the number of times a PDF has been digitally signed and 2) if the signature(s) are valid.
Official response
Mario at GemBox
Hi,
This feature request has been implemented and is available in the latest versions of GemBox.Pdf:
https://www.gemboxsoftware.com/pdf/examples/c-sharp-vb-net-pdf-digital-signature-validation/1105
Regards,
Mario