PDF.js 4.10.38 (legacy build) from Mozilla, Apache License 2.0 (LICENSE.txt).
https://github.com/mozilla/pdf.js - the npm package pdfjs-dist, files legacy/build/pdf.min.mjs and
pdf.worker.min.mjs, unchanged.

The Library Assistant serves them at /pdfjs/ so a phone or computer can draw a book page itself, to print
it as a picture on the receipt printer (print.js), with no other program needed on the Pi.
