The first idea.
The smaller format would be preferred. How to make the size of the voucher is a credit card or something? Automatically. It should work automatically. Clients do not have the nerve to adjust printing options. Some do not know it.
Would you rather pdf format do the same thing but with a jpg/png picture? Everything is the same. But the plugin works png or jpg images. Placed on them: first and last name, voucher number. Print and voucher is in your hands.
This would be awesome.