Outlook 365 corrupting Adobe PDF attachments

Recently a corporate client has been complaining of Outlook 365 corrupting Adobe PDF attachments on Windows 10. In some cases they are able to open the PDF attachment fine. But they are not able to open it another time and get a corrupt error warning. The error that appear is "An unexpected error has occurred" and "there was an error opening this document. The file is damaged and could not be repaired". Other error messages include "Adobe Acrobat could not open 'file.pdf' because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded)."
Outlook 365 corrupting Adobe PDF attachments

Error Status

Live StatusResolved
Assigned TeamsMicrosoft 365, Adobe
ISMS TriadAvailability
ErrorMicrosoft Outlook – The operation failed.
Microsoft Outlook The operation failed

Fixes for Corrupt Adobe PDF Attachments in Outlook 365

We have spent some time troubleshooting issues in Outlook 365 to repair Adobe PDF corruption. We are currently working with our Microsoft 365 support & Adobe support teams to resolve the issue. We are still investigating this issue and will provide further updates.

Below are the solutions we have tried so far to resolve the corrupt Adobe PDF issue in Outlook 365.

Create a new Windows 11 user account

The final solution to resolve PDF corruption in Outlook 365 for our business  client was to create a new Windows 11 user account

Follow these steps to create a local user or administrator account in Windows 11:

  1. Select Start  > Settings  > Accounts  and then select Family & other users. (In some versions of Windows you’ll see Other users.)

  2. Next to Add other user, select Add account

  3. Select I don’t have this person’s sign-in information, and on the next page, select Add a user without a Microsoft account.

  4. Enter a user name, password, or password hint—or choose security questions—and then select Next

You may need to assign this user to the administrator’s group for additional control. Speak to our IT support team in Melbourne if your business needs help.

create a new Windows 11 user account

Setup a new Outlook profile

A common fix for corrupt PDF files in Outlook is to set up a new Outlook 365 profile on Windows. This can work for both Windows 11 and Windows 10. It’s very simple to implement and takes just a few minutes to complete.

Follow these steps to make a new Outlook profile:

  1. Open Outlook and Select File
  2. Account Settings > Manage Profiles
  3. Select Show Profiles > Add
  4. Enter a name (i.e. NEW) > OK
  5. Enter your email  address and password > Next > Finish

If you are using Microsoft 365 Business you may be prompted to authenticate using your authenticator app for your mailbox. You will also have the option to add additional mail accounts to your new profile.

Create a new Outlook Profile to stop PDF file corruption

Use Outlook in the web

We are currently advising our client to try using Outlook.com, the web version of the app. We want to see if PDF files are still being corrupted or not. This will isolate emails and PDF files in a web browser and bypass the Outlook.exe application. 

If PDFs continue to corrupt in OWA (Outlook on the Web), there is a problem with Microsoft 365 backend or PDF browser extensions.

As a Microsoft 365 for business customer we have been able to seek additional support. We have raised a ticket for priority support and working with engineers on this issue.

Use OWA workaround

Workaround: Run Outlook in Safe Mode

We have identified that PDF’s are no longer being corrupted when we run Outlook in safe mode. However once we leave safe mode the PDFs are once again corrupted. As a temporary solution please follow the steps below to run Outlook 365 in safe mode:

  1. Shut down Outlook.
  2. Right click on your Start Menu and choose Run.
  3. In the box that comes up type in OUTLOOK.EXE /SAFE.
  4. Click the OK button.

This will launch Outlook in safe mode and you can attempt to open PDF files to see how they respond. If you are still getting a corrupt error it is likely due to the fact that the PDF has already been corrupt due to being opened prior. Newly opened PDF files in safe modem should not corrupt.

Windows 10 fix: Microsoft update KB5026361 corrupting PDF in Outlook

A Microsoft employee has identified that KB5026361 may be the cause of PDF corruption in Outlook on Windows. A patch is expect to arrive in June 2023 but has not yet been sighted. You should look at uninstalling this update to see if your issue is resolved on Windows 10 until the patch is released.

The easiest way to uninstall Windows 10 updates is by following these steps:

  1. Right click on the Start Button and choose settings.
  2. Select Update & Security.
  3. Select Windows Update.
  4. Select View update history.
  5. Select Uninstall updates.
  6. Find KB5026361 in the list and select and click uninstall.
Uninstall KB5026361 to fix PDF corruption in Outlook

Update to the latest version of Adobe Acrobat Pro

A solution that has worked in the past was updating to the latest version of Adobe Acrobat Pro. This can fix bugs and resolve API issues between other applications. 

However, our Adobe support team was not able to resolve the Outlook PDF corruption with a simple software update.

The quickest way to update your Adobe software is by following these steps:

  1. Open Acrobat Pro and choose Help > About Adobe Acrobat. Note your product version.
  2. Go to the Downloads page.
  3. The web page automatically detects your OS and Reader version.
  4. If the web page indicates that a newer version is available, choose Install Now.
  5. Click the downloaded file and follow the instructions.
Update Adobe Acrobat Pro 2022

Help with Microsoft 365 for business

Intuitive Strategy has IT support technicians in Melbourne who work with businesses to set up Microsoft 365, streamline e-mail communication and protect their OneDrive. Our team of Microsoft 365 experts assist with user on-boarding, maintenance and security.

Give us a call today on 1300 776 334 for unbiased advice and service.

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