Document Template Save PDF to field in Record API Pipeline

I have been wracking my head all day on this.  I was reading Generate Documents from your records in your app where it says "However, you can also create API calls and use Pipelines, code pages, or custom integrations to generate documents. Each part of the formula represents an API parameter.".  I was using Restful "Generate a Document" and was able to make a request:

How do I get the output of making a request or basically the document template for this record as a file attachment in the record?  I tried using:

<qdbapi>

<rid>1700</rid>

<field fid="22" filename="Model_T.jpg"> Base64 encoded file content</field>

Thank you so much!