>PDF forgery is striking because it’d be so easy to do: find a useful research paper, edit it in any of the many PDF utilities, upload anywhere, wait for people to copy it (as they do), then take down yours; now you have an authoritative peer-reviewed research paper floating around the Internet with no links to you, in the perfect crime. (Or better yet: upload it directly to Libgen/Sci-Hub and let everyone else redistribute it.)

Seen as (unsigned) PDFs are basically images of documents, it's wild to claim that there are no forgeries, anyone doing a good ole fake document, fake diploma, fake wire transfer, fake articles of incorporation, etc... is using a pdf for faking. A nigerian prince scam sending an attachment mentioning 15.000.000$ locked up in inheritance would constitute a PDF forgery.

Gwern is talk about editing an existing pdf. Less so about creating one from scratch.

> There is plenty of incompetence, fraud, and malice online, often in PDFs… but only new PDFs. I can’t think of a single fraud accomplished by editing a real PDF & just uploading it for Google Scholar etc. or where I’ve been burned by even mislabeling.