This is a clickbait, sensationalist headline. “Saving a PDF with Preview in Big Sur can corrupt OCR text added by a third-party program” is more accurate.
I've never used any editing features in Preview (I mean it's called "preview" so...) and reading the title I thought this meant it was mangling files even by opening them which would have been super scary.
As for non-Acrobat software mangling PDFs after editing... Well that's much less surprising. I've even had Acrobat mangle stuff in PDFs after editing...
I understand the (fairly common, in these comments) viewpoint that this is the fault of the "third-party program", but since the PDF is readable up until Preview touches it...I find it hard to come around to the viewpoint the third-party program is relevant. Readable bytes -> Preview -> unreadable bytes is my mental model so far.
Edit: absolutely unacceptable this is downvoted to -4. I've observed for a couple months that participation in Apple-related threads, outside indignation that Apple was involved in the discussion at all, gets down to -5 before getting back to -1 a day or two later. No matter what tone is used, this happens, and it makes the problem even worse in the long run. Been here 10 years, always been a _slight_ problem, but over the last year, it's virtually impossible to participate without continuing to slowly destroy my 11 year old account. Not sure how much longer I can keep trying.
PDF is not a bitmap, it’s a script like HTML or JS.
People understand browser incompatibility but some how this is unconscionable.
No reason why you can't just run this through ABBYY FineReader again and get the exact same OCR you got the first time, so I think "irreversible" is definitely a stretch.
There's a big difference between "read-only operation is mangling files" vs. "PDF writer is buggy".
For one, your "mental model" is off because you assume that the first part of "readable bytes" is accurate. Without actually seeing the PDF in question, you don't know if the "readable bytes" are actually corrupted and Preview is fixing them to make them readable. That would mean that Preview is actually correct in its behavior and the source document is what's flawed.
On the tail end of your mental model, then, is another assumption which is that this results in "unreadable bytes" but that's not accurate either. The PDF that results from a save in Preview may be accurate to the PDF specification and is perfectly readable as a PDF in any PDF application/reader. What's no longer readable is the extra content that was originally in the file that may not have been saved correctly, in-spec, or may have been corrupt to begin with.
A big hint as to what's going on here, now that I've had some time to review this, is that the "corruption" happens consistently - the letter "a" is always replaced by the same "corrupted" character, the letter "b" seems to be consistently replaced with the same character, etc. That points, in my opinion, to a lookup that's no longer correct. What side of that lookup is bad is hard to say without seeing the file in question.
Keep trying, just with a new account every few months are so. HN has no privacy controls, we must add our own.
There are a chance that write goes wrong, but Preview is much more geared towards read than write.
This doesn't excuse Preview, but its name is suggestive enough.
If the behavior changes, that's not on me, that's on Preview.
I don't have any issue with this today on my Mac, but I'm glad I didn't upgrade to BigSur. I almost did.