Thanks Blake, that is basically the route I am taking now.  Way more steps but it should alleviate some of the headaches we are having with our external users.

Hi Erik-

Unfortunately, there's no easy way to do this. I have some processes that work how Steve describes, embedding the doc in an iframe. Alternatively, we just set up a new process where we email the PDF documents to the person for review, then they just indicate in Forms if they're good or need to be modified. Not necessarily easier, just another option depending on what you're comfortable with.

Unfortunately, these are going to be public forms, is there a way to move a public user to another form page/process?  Or is it after the message pops up redirect them to another forms page, but how would you pass something so that the new form would know what document they are talking about?

Erik, it will depend on how creative you want to get. While still not as good as being able to send the PDF back to the Forms process, you could save the instance ID of the form in a database table and send an email to the public user that submitted as Pieter mentions. In the email it would include the attachment of the filled-out PDF and a link to the same or different (public facing) form. The data from the 1st form could be saved to a database table as well. In the email you could include the Instance ID (call it whatever you wanted in the email) and on the form ask for it and another piece or two of information and then ask the user if everything in the PDF was accurate. If not, you could display all of the fields, populated from a database lookup with the originally submitted information and allow them to submit again.

Instead of sending the PDF in an email you could do as Steve says and embed it in the form.

This may not be the best solution depending on what type of information you are collecting on the form. If it is sensitive in nature, it may not be the best idea since someone could start plugging values in the fields to see if they get results.