During one of the mass exodus events from Reddit to Lemmy, a lot of people started using these tools they would install to automatically scrub and obfuscate their Reddit comments and posts history. Often these tools would replace posts with random letters and even nonsense links because there was suspicion that outright deleted posts could be detected and then programmatically restored if Reddit really wanted to get that user content back.

I suspect these tools probably exist for Lemmy as well and you are seeing users with long comment histories use them because those also happen to be the users who have a lot of previous content to cover up/obfuscate to maintain/ensure their own privacy.

There are a bunch of online tools that are free and let you upload a PDF to have it go through OCR.

Just Google “Free PDF OCR” and click through all the ads to upload, then give them a temporary email address to get a download link to the finished product.

Hot tip: There are free temporary email address sites too, if you need one to avoid getting on their ad lists.