🔍 The Symptoms

🧠 Root Cause

The issue occurred because the files were opening with Microsoft Office 2021 installed on the device. While Office 2021 can open Office documents, it does not provide the same continuously updated Microsoft 365 cloud-connected feature set as Microsoft 365 Apps for enterprise or Microsoft 365 Apps for business.

For modern OneDrive and SharePoint co-authoring, the local Office client must support the required collaboration features, authentication experience, AutoSave behaviour, and cloud file locking mechanisms. In this case, Office 2021 was causing files to open in read-only mode or appear locked when accessed through File Explorer.

🛠️ Step-by-Step Resolution

1. Open microsoft365.com
2. Go to OneDrive
3. Browse to the affected file
4. Open the file in Word for the web, Excel for the web, or PowerPoint for the web
5. Ask another user to open the same file and test co-authoring
6. Confirm whether both users can edit the document at the same time

1. Open File Explorer
2. Browse to the user’s synced OneDrive folder
3. Open the affected Office file
4. Check whether the file opens in read-only mode
5. Check whether the user receives a file lock message
6. Test another Office file from the same synced location

1. Copy the affected file to a local folder such as Documents or Desktop
2. Open the copied file using the installed Office desktop application
3. Edit and save the file
4. Reopen the file and check whether the read-only behaviour persists

GUI Method

1. Open any Office application such as Word or Excel
2. Go to File → Account
3. Check the product name under Product Information
4. Confirm whether the installed product is Microsoft Office 2021, Office LTSC 2021, Microsoft 365 Apps for enterprise, or Microsoft 365 Apps for business

PowerShell Method

$OfficeConfigPath = "HKLM:\SOFTWARE\Microsoft\Office\ClickToRun\Configuration"

Get-ItemProperty -Path $OfficeConfigPath |
Select-Object `
    ProductReleaseIds,
    ClientVersionToReport,
    UpdateChannel,
    Platform,
    InstallationPath

$OfficeUninstallPaths = @(
    "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*",
    "HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*"
)

Get-ItemProperty -Path $OfficeUninstallPaths -ErrorAction SilentlyContinue |
Where-Object {
    $_.DisplayName -like "*Office*" -or
    $_.DisplayName -like "*Microsoft 365 Apps*"
} |
Select-Object DisplayName, DisplayVersion, Publisher, InstallLocation

GUI Method

1. Select the OneDrive cloud icon in the Windows notification area
2. Select Help & Settings
3. Select Settings
4. Confirm that the correct work account is connected
5. Confirm that there are no sync errors
6. Check whether the affected folder is syncing correctly

PowerShell Method

Get-Process OneDrive -ErrorAction SilentlyContinue |
Select-Object Name, Id, StartTime

$OneDrivePath = "$env:LOCALAPPDATA\Microsoft\OneDrive\OneDrive.exe"

if (Test-Path $OneDrivePath) {
    (Get-Item $OneDrivePath).VersionInfo |
    Select-Object ProductVersion, FileVersion
}
else {
    Write-Host "OneDrive.exe was not found in the expected user profile path."
}

Option A — Settings App

1. Open Settings
2. Go to Apps → Installed apps
3. Search for Microsoft Office 2021
4. Select Uninstall
5. Restart the device after the uninstall completes

Option B — Control Panel

1. Open Control Panel
2. Go to Programs → Programs and Features
3. Select Microsoft Office 2021
4. Select Uninstall
5. Restart the device

1. Go to microsoft365.com
2. Sign in with the user’s work or school account
3. Select Install apps
4. Download and install Microsoft 365 Apps
5. Open Word or Excel after installation
6. Sign in with the user’s Microsoft 365 work account
7. Confirm activation under File → Account

1. Open the affected file from File Explorer
2. Confirm that the file opens in edit mode
3. Ask another user to open the same file from OneDrive or SharePoint
4. Confirm that both users can edit the document at the same time
5. Confirm that AutoSave is available and enabled
6. Verify that the file no longer opens in read-only mode
7. Confirm that the file lock error no longer appears

✅ Validation Checklist

💡 Best Practices & Recommendations

• Use Microsoft 365 Apps for enterprise or Microsoft 365 Apps for business for the best OneDrive, SharePoint, and Teams file collaboration experience
• Avoid mixing perpetual Office versions such as Office 2021 with Microsoft 365 cloud collaboration workflows where real-time co-authoring is required
• Keep the OneDrive sync client and Microsoft 365 Apps updated to ensure compatibility with the latest collaboration and file locking features
• Store shared business documents in SharePoint Online or Teams-connected document libraries instead of relying on local-only file copies
• When troubleshooting file lock issues, always compare browser behaviour with local Office behaviour. If the file works online but fails locally, the issue is usually related to the Office client, sync client, authentication, or local cache

📝 Conclusion

📚 References & Further Reading

• 🔗 Deployment guide for Microsoft 365 Apps — Microsoft Learn
• 🔗 Overview of update channels for Microsoft 365 Apps — Microsoft Learn
• 🔗 OneDrive sync health reporting in Microsoft 365 — Microsoft Learn
• 🔗 Use Group Policy to control OneDrive sync settings — Microsoft Learn