Wanting to redact information is not a subset of PDF knowledge. Understanding how PDFs work is not a prerequisite of desire to redact information. Lots of people have only the most basic rudimentary understand of how PDFs work, how Adobe works, and the limits or capabilities.
A lot of people don't even know you can print to a file instead of paper. Not sure why you're surprised about that, after all the standard method for all formats is "save as" or "export" and it's reasonable to assume those two options include all possible ways to save a file. It's a UI quirk that goes against user expectations.
Recently discovered a manual forr some home appliance with a clear Word comment along with username, seems like slipped in when the manual was translated.
