Position Extraction with 3rd party PDF not detecting signature field

Hi, Is there any requirement on the PDF so that Position Extraction is captured by the REST API? The problem I'm having is that Im working with a 3rd party which delivers a PDF with Signature Fields in the PDF. I've requested that they add a specific convention on the Position Extraction naming Convention for the Signature Fields. We are using the same convention on a PDF edited with Form Fields in Adobe Pro with text Fields with our naming convention. When we print out forms, the signature fields are picked up by the ESL API....but when we append the 3rd Party PDF, the fields are not picked up. One thing I noted as difference is that the PDF was edited with another NON ADOBE software. I can send the PDF privately. Thanks