How to add digital signature to existing PDF document

This feature is since XFRX 18.1

* create PDFL#INIT object
loSession=EVALUATE([xfrx("PDFL#INIT")])
* open existing PDF document with append mode
loSession.createDocument("BASE-UNI.pdf", .T.) 
* Add digital signature
loSession.DigitalSignature("testeqeus.pfx","eeee",2, "testing name", "testing contact info", "testing location", "testing reason") 
* Finish document
loSession.FinishDocument()