How do I reference a hosted docx rather sending every time when creating a pdf (document generation)

Use case:

I am creating a document from form values captured via a webform which I can parse out as json and send across.  I am using https://cpf-ue1.adobe.io/ops/:create

Where I am struggling is to specify anything other than a local docx file.  Ideally I would like to just pass across a reference url to a docx hosted on acrobat.adobe.com.  At the moment I have to send the docx as well as the json data which seems inefficient.