Hi there,
Understood what you want to achieve and I know exactly what to do to achieve it. I can write it in PHP or JS, I believe in your case PHP is preferred since I believe the receipt is generated on the server.
I'm happy to share more details on the techniques I would utilize in chat.
My script would accept a string as an input, and it would output an image. Image would contain the input text but treated in such way that it looks like it has been printed. Then you can add that image to your PDF receipt just like you currently do with plain text. My bid doesn't include the integration bit, just a standalone script doing what I described. If you need me to integrate it into your existing system I can do that too but I will need to update my bid, and would have a few questions.
Regards,
Julijan