It's done! Network printer and scanner, hosted by a Raspberry Pi Zero W. I used CUPS to host the printer, but the scanner was much more difficult. I installed apache2 on the Pi to host a HTML front-end that I wrote. Once you set up the scan, the front-end makes an AJAX call to a PHP script, which then calls my Python script that does the scanning and converting. Once that's done, it returns the file name via the AJAX call, then the front-end downloads the scanned PDF on the computer. I even managed to impress my girlfriend, who didn't really understand what I was doing until I showed her the end result 😄

I might try to pipe the output of the conversion straight back via AJAX, to be downloaded without a second call.