Is it possible for users to add a document when form is submitted?

Is there a way that someone filling out a form can add a document to the form when it is submitted? 

I am not sure if I have understood your question correctly. Do you want to allow your users to upload a document and then submit the form?

Yes it is possible to achieve your requirement by adding "File Upload" field in form. Please check the screenshot below:

Hope this helps.

Do get back to us if you meant to ask something else.