Purchase order document printing

There was a case that we had recently whereby a supplier was requesting monies to be paid to them. The supplier does not exist on our system. Seems like “someone” got hold of a very old PO and edited it and defrauded this supplier.

Is there a way that we can make our PO not to be editable

Can we perhaps think of inserting a watermark ,  making it password protected and non-editable? Or even sending a secure link to suppliers that when they click on it, they see the PO or even a QR code?

Regards

James