@Julie Cadman you can do this with Google Apps Script:
https://stackoverflow.com/questions/36053198/convert-pdf-to-doc-with-google-script-editor
I created a framework for automating Trello with Google Apps Script that would allow you to detect an attachment added, perform the conversion then attach the document as Word pretty easily:
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.