Instructions
You can use a PDF Stamp to number your output pages.
Documentation on PDF Stamps:
https://help.nintex.com/en-US/docgen/docservices/#docgen-sfdc/Services/manageDDP/StampYourDDPs.htm
Example:
Documentation on PDF Stamps:
https://help.nintex.com/en-US/docgen/docservices/#docgen-sfdc/Services/manageDDP/StampYourDDPs.htm
Example: