Symptoms: You are trying to open a file that was either emailed to you (or recently composed by yourself on a computer running Office 365 desktop versions), and you receive the error "the file is corrupt and cannot be opened" or "...found a problem with content - if you trust the source click Repair". If you save that file to your desktop and right-click it, you may find that it appears "blocked". Solution to this is provided below.
1/ HOW TO UNBLOCK A SINGLE FILE
In explorer, right click the file, select Properties.
Untick "Blocked"
2/ HOW TO PREVENT THIS PERMANENTLY
OPTION ONE: EDIT FILE BLOCK SETTINGS
Open the affected application (Word, Excel, Powerpoint)
Click on: File > Options > Trust Centre > Trust Centre Settings
In Trust Center settings, select Protected view and un-check the following boxes:
Enable Protected View for Files originating from the Internet
Enable Protected View for Files located in potentially unsafe locations
Enable Protected View for Outlook attachments
Save the changes and close the Office program.
Repeat for all effected programs.
The files should now open without any issue.
OPTION TWO: ADD A NEW TRUSTED LOCATION
Open the affected application (Word, Excel, Powerpoint)
Click on: File > Options > Trust Centre > Trust Centre Settings
In Trust Center Settings, select Trusted Locations
click Add new location
Select the drive in which you saved your word files
check the “Sub folders of this location are also trusted” checkbox
click Ok to save your changes.
Save the changes and close the Office program.
Repeat for all effected programs.
The files should now open without any issue.