Nice vid. If you didn't know the early history of PGP, the OG user's guide served as a great introductory read to the core concepts of encryption / PKI.
https://en.wikipedia.org/wiki/Pretty_Good_Privacy#Early_hist...
https://ia601407.us.archive.org/9/items/pgpguide.-lst/PGPGUI... (35pp, .txt) https://web.archive.org/web/20201205180542/https://www.tech-... (same, .pdf)