I made a PDF diff tool for myself for one of my internships >10 years ago.

One of my responsibilities was to get sign-off on any changes engineers made to schematics. (It was a really bad internship! I ended up automating a bunch of stuff for them because my actual job was mind-numbingly boring.)

After the first few times comparing PDFs of schematics by eye, I said screw it and wrote a tool to export to PNGs and then compare them pixel-by-pixel. It saved me a ton of time and my sanity.