Hi Clark,
What I have found, based on the link Phil supplied and an answer to an issue I had with the onFormSubmit, is that you will need to set it up this way:
1. Form - Link it to a Google Sheet
2. Sheet - Attach your script to this sheet and setup an Installable Trigger to call your function with the trigger onFormSubmit. This script will receive the response as part of the event and with that you can create your document and insert data from the response.
3. Doc - Do not attach a script.
Hope that helps.
Ron