provide pdf modification as a zesje service
Generating a pdf with multiple uniquely QR-coded copies via latex is slow (because latex isn't designed for computing QR codes), error-prone (because we are performing low-level latex hacking), and it is only possible in latex (by construction).
If we use any library for manipulating pdf files (like e.g. this one or one of the alternatives), we could allow users upload a template pdf with sufficient space at the top margin and slap our own qr code or page markup on it.
Edited by Anton Akhmerov