P21 Printing a Certificate of Conformance with a packing list

We are trying to automatically print a Certificate of Conformance PDF when a pick ticket or packing list prints (I will settle for either). It cannot be done at the item maintenance level because multiple customers order the same thing and we only want this to print for one customer. I thought customer part number maintenance would be the place to do it but this mandatory checkbox is not selectable. I think that is what we are missing. Am I barking up the right tree? Can anyone confirm this box is selectable on their config?