Preview's "Markup" not working with other PDF viewers?

[macstatic]

I often use Preview's "markup" feature to remove personal information in PDF documents by overlaying the areas I want hidden with black rectangles, like this, then save the document:

I recently sent someone such a PDF file, and in my webmail's "sent" folder clicked on the PDF attachement only to be shocked by the fact that all of those black rectangles were gone, leaving the entire contents visible!
This was is the webmail's preview feature in the browser. So I downloaded the same document on to my Mac desktop, double-clicked it to view it with Preview, and the black rectangles were back!
I can only conclude that the "markup" feature is only good with Preview.

I read some comments somewhere about this being a bug -if so, is it something that has affected several MacOS versions?
The PDF I discovered with this problem was done in MacOS 10.15 Catalina, but I've edited and shared lots of PDFs like this with people within MacOS 10.14 Mojave, so I'm worried a lot of private information has been shared unwillingly.

So how do I safely edit a PDF document in the same way, but be sure it stays that way regardless of OS platform (Mac, Windows, Linux etc.) and PDF viewer?

 

[sahnert]

recent versions of preview have a redact tool that is designed for this job. According to the documentation the redactions become permanent on closing the document.

“Select text to permanently remove it from view. You can change the redaction as you edit, but once you close the document, the redaction becomes permanent.”

 

[chown33]

Overlaying text in PDFs with black boxes DOES NOT redact the text. All it does is draw something else on top of the text. The text is still there, as you've discovered. Anyone with a moderate amount of knowledge of the PDF format can recover the underlying textual data.

It wouldn't surprise me at all to learn that a few judicious prompts to an AI would give a step-by-step guide on how to do it, and exactly which tools to use.

The same goes for SVG images, and a host of other scalable or vector formats.

 

[FreakinEurekan]

It’s not “only” Preview, but some apps might not display annotations. Haven’t found any myself but I’m not really looking for them.

As others said, using annotations to prevent someone from seeing text is a bad idea. Use the “redact” feature if you have a new enough Mac, or a 3rd party app with redact ability if you don’t, or take a screenshot of the document with the info blocked and send the screenshot.

 

[macstatic]

Thanks to all for clearing up my misunderstanding. I really had no idea!
I was 100% sure that the "black boxes" overlay in Preview would do the trick because having saved the PDF document then opened later on I'd notice it was no longer possible to edit those annotiations (strangely this isn't always consistentas I just tried it and it was possible to re-edit an annotiated, saved, then closed and reppened PDF. Maybe it has something to do with what's in Preview's cache after a reboot etc.
Apparently not everything that meets the eye is what it seems.

I'm currently trying to find a solution for MacOS 10.14 and 10.15 (I also had a closer look at Preview, but as people have stated here already, the redact feature is only available with more recent versions of MacOS/Preview, so not much luck there), but haven't found much yet.
There's the RapidTools website with its redact feature which is free and claims to redact PDF files (that you drag&drop to its window) without uploading and sharing any data, but I'm not sure I feel comfortable trusting that claim.
PDFsimpli is another similar online browser tool.
I haven't been able to find anything free so far (which works with my OS versions), but will keep on looking. According to the Redacting sensitive info thread in Apple discussions I will have to resort to commercial software for MacOS Catalina or earlier.

Until then, I guess the guaranteed safest method of redacting anything sensitive is to print out the PDF file (with the black boxes done with Preview, or manually using a black marker on the printout), then scan the printout again and convert it to a PDF file. Quality loss and a hassle to do: yes, but at least I won't be risking that I share social security numbers and so on.

 

[chabig]

I guess the guaranteed safest method of redacting anything sensitive is to print out the PDF file (with the black boxes done with Preview, or manually using a black marker on the printout), then scan the printout again

I don't think you have to go that far. Use Preview's redact tool, and then print to PDF as a final step.

 

[macstatic]

I don't think you have to go that far. Use Preview's redact tool, and then print to PDF as a final step.

Yes, but I don't have a version of Preview which has the redact feature (I'm still on MacOS 10.14 and 10.15).

But perhaps you meant that I use the black boxes (press Preview's "Markup" button first) as I've always done (see the screenshot in my very first posting in this thread), then select "File"-Print" and finally "Save as PDF" in the printer dialog?
Will this "burn in" the black boxes into the PDF as opposed to having it as a separate (and removable) layer?

How can I best check PDFs to see if they actually have been redacted properly to make 100% sure I'm not sharing any sensitive info?

 

[chabig]

But perhaps you meant that I use the black boxes (press Preview's "Markup" button first) as I've always done (see the screenshot in my very first posting in this thread), then select "File"-Print" and finally "Save as PDF" in the printer dialog?

I used to think that would work, but I am not sure anymore. I think it hides the data so it cannot be viewed but the data remains in the file, subject to retrieval by someone savvy enough to dig it out of the code.

If you can’t redact, printing and scanning, or exporting to an image format will be safer.

 

[FreakinEurekan]

Until then, I guess the guaranteed safest method of redacting anything sensitive is to print out the PDF file (with the black boxes done with Preview, or manually using a black marker on the printout), then scan the printout again and convert it to a PDF file.

Just screenshot it.
Command-Shift-4 and drag to screen confines
-or-
set Preview to full-screen, then Command-Shift-3 to capture the whole screen
-or-
I think this will work on Catalina... Command-Shift-4, then press Space bar. If the icon turns into a Camera, you can click on a window (Preview) and it'll screenshot just that window.

 

[NoBoMac]

I think it hides the data so it cannot be viewed but the data remains in the file, subject to retrieval by someone savvy enough to dig it out of the code.

This. And don't need much skill. From Tahoe, annotated, saved as PDF, select, context menu:



ADD: and can select, copy/paste the text in Adobe as well. Guessing if one uses Chrome to view, might be even more lax as I have used it in the past to bypass the flag that controls modifying of a PDF (in my case, generate a new PDF in Chrome and then edit in Preview to delete unneeded/wanted pages).

 

[splifingate]

How can I best check PDFs to see if they actually have been redacted properly to make 100% sure I'm not sharing any sensitive info?

Print; black those items out; scan->PDF; share.