Print At Home

We launched Print At Home ticketing last evening and have just discovered that when the end user opens the pdf for their eticket, they are able to edit the contents in the ticket element fields.  They are not able to save the file, but they could, for example, change their seat and then print the revised form.  We expect that if someone were to do this, the barcode would still indicate the correct/original seat.  And I also have set our system so that copies of every PAH ticket order goes to a mailbox that I manage, so we could pull up a copy of the original order to verify the original contents. But, does anyone know how to restrict the form from being edited?  I tried checking the "locked" box in the field properties but that still allowed editing.  And I also set a password to restrict changes, but that then prevented the form from being generated when a ticket order is placed.