PDF read-only protections in Preview with Big Sur

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Level 1

8 points

PDF read-only protections in Preview with Big Sur

On macOS Catalina, if I tried to save a PDF that I had modified in Preview, but which had a PDF protection policy with the read-only flag set, I was blocked from saving this change by a warning or error to the effect of "this file cannot be saved because it has been modified". This is the behaviour I would expect for a PDF which does not allow modifications.

However since I installed Big Sur, I'm no longer blocked from modifying or saving/overwriting PDFs in Preview which have been set to read-only.

1) Is it a bug that Big Sure does not respect the protection flags set within the PDF? And if so, can we anticipate a patch/fix for this?

2) What flags/policies can I set within the PDF that will block users from being able to modify the original file with Preview on Big Sur?

For clarification, I am talking about the protections/flags that are set internally in the PDF, and not file system permissions (read-write-execute).

I am attaching a screenshot of one warning which I used to see on Catalina but no longer on Big Sur:

I am also attaching a screenshot of the protections summary shown in Adobe's PDF reader for the PDF which Preview is allowing me to modify and overwrite:

MacBook Pro

Posted on Apr 26, 2021 7:04 AM

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Answer 1

Barney-15E

Level 10

122,126 points

Apr 27, 2021 9:06 PM in response to absicola

Specifically in this case, Preview edits the content of a PDF that is digitally signed with a cryptographic signature.

Do you mean a fillable form?

Preview does not "Edit" a PDF at all. It is not a PDF editor. You can add annotations and enter information in fillable fields. And, apparently you can move the digital signature around.

Preview does not support many of Adobe's PDF capabilities.

You'd have to provide feedback to Apple about the problem if you want to make them aware of it.

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Answer 2

Barney-15E

Level 10

122,126 points

Apr 26, 2021 8:37 AM in response to absicola

As Preview cannot alter a PDF, it is always read only. You can add annotations, but that doesn't alter the content of the PDF.

Preview is not a PDF editor.

Can you print or extract individual pages from the document?

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Answer 3

absicola Author

Level 1

8 points

Apr 27, 2021 12:54 PM in response to Barney-15E

Thank you for your comment.

Specifically in this case, Preview edits the content of a PDF that is digitally signed with a cryptographic signature.

I understand that Preview does not support cryptographic signatures, which is why I want to stop users from being able to corrupt the digital signature when they open the signed PDF in Preview and find that it auto-saves and overwrites the content incorrectly. This issue is documented in a few forums online.

If I open a signed PDF in Preview on Big Sur I am even able to click + drag the signature box to another location and save it, which alters the content of the signature in the PDF. When I then open it in Adobe's PDF Reader, I find that the signature is no longer valid.

The simplest solution would be for all users to avoid opening the PDF in Preview, however this is not a realistic solution because I am not able to communicate this to all parties sharing/viewing the signed documents. The next best solution is to lock the PDF from modifications, and this worked on Catalina but no longer on Big Sur.

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PDF read-only protections in Preview with Big Sur

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