How to modify a document after submitting it for printing (add a QR code to print)?

Question

Seal

I suppose you need to create a virtual printer that will modify the document (add a QR code there) and then print a real printer. Can you tell me the best way to implement this? Maybe there is some Opensource project that can be customized for this task?

Answer 1

the virtual printer should, in my opinion, print itself. As options - you can write your own driver for a real printer, or intercept system calls related to the print queue. But best of all, get the content before printing, modify and send to print.
But a virtual printer can also be used. Firstly, if you write it yourself, then he will be able to edit the document and drop it into a file, for example, PDF, then print the PDF. Secondly, you can take a ready-made PDF printer, print on it, then open PDFs, edit them and send them to a real printer for printing.