An old manager used to like giving me PITA (Pain In The Ass) Projects that solved something useful, but were a bit arcane for some reason or other. A couple were printer-related, for our customers.

One customer had a cheque-printing routine that used a blob of HP PCL (Printer Control Language) for some reason when printing these cheques. The blob included image date of the finance person's signature, and they'd changed executives. We didn't have information about how this blob had been created initially, but I was able to pick it apart with a printer manual and hexl-mode in Emacs. That let me edit hex data which could still change size, and replace one image with another.

Another customer had salt mines, which are very corrosive environments, and you didn't want much in the way of computer gear there. They needed to be able to print shipping sheets from head office, ideally without any PC or server on-site. Using a modem and a dot-matrix printer with a serial interface, I figured out a way to connect and send a print job that worked. Not sure if they ever ended up using it though.