If you plan to use PyPDF2 for encrypting or decrypting PDFs that use AES, you will need to install some extra dependencies. Encryption using RC4 is supported using the regular installation.

This solution was posted a couple years back (see below) and still fixed the issue by installing PyPDF2-2.12-1 to replace PyPDF2-3.0.1. So - easy fix, but figured I would make note of it! Insalling ...