I thought this might have something to do with printer steganography [1] but not if they are just X-raying the paper. Also I'm not sure whether that practice is

I thought this might have something to do with printer steganography [1] but not if they are just X-raying the paper. Also I'm not sure whether that practice is ongoing--I haven't heard anything about it for years. [1] https://en.wikipedia.org/wiki/Printer_steganography https://en.wikipedia.org/wiki/Printer_steganography