I'd say either CSV or JSON so you can still look for data easily
Plain text could still work but it would be hard to search for stuff. PDF sounds evil
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time (tm) ). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
I'd say either CSV or JSON so you can still look for data easily
Plain text could still work but it would be hard to search for stuff. PDF sounds evil
I'd save as HTML and then run something to convert it to markdown or some other type of plain text.
Why do you want to delete a post history?
Punch cards.