Outlook for Mac corrupting attachments..

Hi,

Thank you for your response and for looking into this. Here are my answers to your questions:

1. Does this occur with all PDF attachments or only with PDFs generated by a specific application or sender?

The issue is NOT specific to any particular sender or PDF type. It occurs randomly with different PDFs from different senders. Some PDFs open fine and some do not — there is no pattern I can identify based on sender or PDF source.

2. If another user running New Outlook for Mac receives the same email, do they experience the same behavior?

I have not been able to test this with another Mac user yet. I will check with a colleague and update you.

3. When comparing the PDF downloaded from OWA and the PDF downloaded from New Outlook for Mac, do the file sizes match?

I have not compared file sizes yet. I will do this and update you with the results.

4. SHA-256 hash comparison:

I will compare the hash values of the same PDF downloaded from OWA vs New Outlook for Mac and share the results here.

Additional Information:

• The same PDF attachment received on Apple Mail (Mac Mail) on the SAME MacBook opens perfectly without any issues
• The same PDF downloaded via Outlook Web App (OWA) also opens correctly
• Only New Outlook for Mac desktop app shows the corrupted/overlapping content
• This happens randomly — not with every PDF, not from a specific sender
• I have already tried: updating Outlook, clearing cache, changing default PDF viewer, removing macOS quarantine attribute

Could this be a rendering or font-handling issue specific to New Outlook for Mac? Since it happens randomly and not with all PDFs, could it be related to how New Outlook for Mac processes certain embedded fonts or specific PDF structures during download?

I will update this thread once I have the file size and hash comparison results.

Thank you for your continued support.

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Hi Krishna Chaudhary

Based on your description, the PDF file itself does not appear to be corrupted. The same attachment opens correctly when downloaded from Outlook on the web (OWA) and when received through Apple Mail on the same MacBook. This suggests that the original attachment remains intact and that the behavior may be specific to how the attachment is being handled within New Outlook for Mac.

I also found discussions from Apple and Adobe communities where users reported situations in which PDF files behaved differently depending on the application used to download or open them. In those cases, the original PDF remained valid, while the issue appeared to be related to local application handling, fonts, or rendering behavior rather than the document itself. However, those reports involved different products and environments, so they should be considered only as related observations rather than a direct explanation for your scenario

*.pdf Could not be opened - It may be dam… - Apple Community

Cannot extract the embedded font (Mac) | Community

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To better understand the issue, could you please share some information:

• Does this occur with all PDF attachments or only with PDFs generated by a specific application or sender?
• If another user running New Outlook for Mac receives the same email, do they experience the same behavior?
• When comparing the PDF downloaded from OWA and the PDF downloaded from New Outlook for Mac, do the file sizes match?
• If possible, can you compare the SHA-256 hash values of both files? If the hashes differ, that will indicate that the file saved by Outlook for Mac is not identical to the version downloaded from OWA.

As a temporary workaround, you may continue downloading affected PDF attachments through Outlook on the web, since that method appears to preserve the file correctly.

I hope this information helps, and I look forward to your response.

I hope you understand that we're not Microsoft support, this is a user-to-user support forum. Moderators have no backend access and cannot directly intervene in Microsoft products. We provide only technical guidance and best-practice recommendations based on reported issues) 

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