It uses Full-Text RSS and PDF Newspaper to extract the article's content and produce a clean HTML copy. It then relies on Headless Chromium to generate the PDF. To avoid situations where an article will use an extra printed page for a small overrun, Simple Print produces 3 PDFs with slighly varying font sizes and keeps the copy with the fewest pages and largest font size.
Simple Print is a website that converts web articles into nice, easily-printed PDF files. It was remarkably effective on the URLs I fed it.