Hi @Eric_D_Miller,
For whatever reason Workfront is not saving the portfolio ID on the Document, but is does save project ID.
If Task on project use Task ID exists and filter per project ID (I would assume the tasks would be on one project)
Please check the screenshot I provided and tested.

Also please note the checkbox "Exclude updates made by this connection" if you have an automation that is uploading the files you will have to disable this checkbox, also if you only want initial upload you should be aiming for only "New Records".
Hopefully this helps.
Best regards,
Ivan Bebek