This will be a digital signature using the class 2 certificate. 

They are providing PdfDocumentSignature action will help with PDF digital signature. You should upload your .pfx certificate in the Certificates folder 

Parameters details -

 Input Parameters :

• certificateFileName - Certificate file name (e.g. ABC), not an extension
• certificatePassword - Certificate Password 
• certificateDirectory - Certificate Directory whatever you can but the default is "Certificates"
• inputPdf - Input Pdf 

Output Parameters :

• signedPdf - Signed document
• errorCode - Error Code 
• errorMessage - Error Message