Applying a digital signature to a PDF

I need to pull a certificate off a smart card and use it to apply a digital signature to a PDF file.  I have software to access the smart card, but once I get the certificate, what is Aspose looking for in the pfx field?  Will the password be on the smart card? We enter a pin number.  Is that it? 

How do I find the signature field on the PDF? 

Sorry for what may be dumb questions.  I am a long time Aspose.PDF user but have had no experience with signing a PDF with a digital signatures. 

Any current examples will be appreciated too.  We have version 9.8. 

thanks

Steve