Did you export the form from InDesign to an Interactive PDF?
Why "one of the fields"?
When I exporting the form from InDesign I choose Interactive PDF.
There is a field where a number needs to be typed in. We would like that number included in the Subject line of the email being sent to Identify what job this information is for.
Not sure that can be done. Maybe someone else on here will have an idea.
By the way, you will need to enable the form so that the user to be able to store the information they add by enabling the facility in Acrobat before you distribute the form.