Hi AndrewG123456,
I’m Jung one of the Independent Advisor and I’d be happy to help you out with your question.
Based on your description, there have some specific Excel files that would get the error message as the following screenshot. May I know if the issue files are related with Outlook? Anyway, have a try with following suggestions to fix the issue.
1.Run the Office Repair Tool.
Press Win+R and type Conrtol Panel in the window
Click uninstall a program under Programs tab
Select the Office version you have installed and click Change button on the top bar
Leave the Quick Repair option selected and click Repair
Check the result after the repair process is completed by opening the issue file in Excel to see if everything back to normal. If the issue persists, try the Online Repair option again.
2.Disable Protected View
Open Excel and click the Options in the bottom-left corner.
Click on Trust Center and click Trust Center Settings
Switch to the Protected View tab and uncheck all options.
Then click OK to save the changes, and check if the issue disappear when opening the files again. But this is only a workaround currently and make sure all files are safe and have a strong antivirus installed on the local PC.
3.Rename the file and change the file type.
May I know if these issue files have been downloaded on the local PC? If so, please check if their file type is .xlsx as the newer Excel format if you are using the latest version of Excel. After opening the file with the workaround you discovered, click File and click Save a Copy. Select the location as you want(local PC is recommended but OneDrive is also good) and rename the file and select another file type.
If the issue persists after trying above suggestions, please share us the current version of Excel on your side so that we could offer some other appreciate support based on your scenario. Open Excel > click File > click Account and share the screenshot here.
You may check this thread for more details:
https://answers.microsoft.com/en-us/msoffice/forum/all/error-message-file-couldnt-open-in-protected-view/c5693143-b353-41b5-b5e9-581090613d55
Kindly check this links as well for the other troubleshooting steps that you can try: https://www.technipages.com/excel-this-file-couldnt-open-in-protected-view
[Fixed] Excel Protected View Editing This File Type Is Not Allowed: 2 Solutions
Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
I hope this information helps. If you have any questions, please let me know and I’ll be glad to assist you further.
Best regards, Jung
