how do I allow submitter to save document and come back to it

I understand that you want to allow your users to save the form so that they can come back and edit and submit the form later. This requirement can be achieved by enabling the Auto-fill feature. Please refer to the guide below that can help you with this.

http://www.jotform.com/help/227-How-to-Enable-Auto-Fill-Feature

Please note that this feature saves the data into the local browser storage of the user so it's required to continue using the same computer and browser. If you need form users to continue later using another device and browser, you may consider using the Session URL method instead provided below:

http://www.jotform.com/help/97-How-to-Save-Forms-to-Continue-Later?

Hope this information helps! Please get back to us if you need any further assistance. We will be happy to help.