When I added a submit button and added mailto:firstname.lastname@example.org then set the "export" values to XFDF to exclude the submit field. When the form is submitted the recipient can see the submit button anyway. Am I doing something wrong?
What do you mean by "...the recipient can see the submit button anyway." What exactly are you expecting? Is the recipient importing the XFDF into a blank form using Acrobat, launching the FDF, or something else?
I created a PDF from InDesign®. Using Acrobat X Pro®, I inserted 2 buttons. One is a clear form button, and the other is a "submit" button. In the properties of the submit button I selected "exclude" both of the button fields. I thought that those two buttons would be hidden when it was sent via the "submit" button. If that is not the case, then what does the "exclude" feature really do?
It means that the _value_ of the field is not sent when you submit _form data only_ (which is the normal way of working). This has no relevance to a submit button, and no relevance when you send a whole PDF (it doesn't delete anything).
It's still not clear to me how the XFDF file is being used. It may be possible to get what you want, but you need to provide more information. Exactly what does the recipient of the email that has the XFDF attachment do with it?