How to Fix 'The File You Are Attempting to Preview Could Harm Your Computer' in 8 Proven Ways

Part 1. What Does “The File You Are Attempting to Preview Could Harm Your Computer” Mean?

This warning appears in Windows File Explorer’s Preview Pane when the system blocks a file from being previewed due to security concerns. It is part of Windows’ built-in protection system that flags files downloaded from external or untrusted sources.

Users facing such issue usually received an error message:

“The file you are attempting to preview could harm your computer. If you trust the file and the source you received it from, open it to view its contents.”

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Is This Warning a Virus or a False Alarm?

In most cases, this is not a virus. Instead, it is a precaution triggered by Windows security policies. However, it can sometimes indicate potentially unsafe files, so you should always verify the file source before opening it.

Which Files Trigger This Warning?

This issue commonly affects:

• PDF files
• Microsoft Word, Excel, and PowerPoint files
• Files downloaded from browsers
• Email attachments
• Files synced via OneDrive or network drives

These files often carry metadata called “Mark of the Web” (MOTW), which tells Windows the file came from the internet.

Part 2. Why Is My Preview Pane Saying “The File You Are Attempting to Preview Could Harm Your Computer”?

Several factors can cause this warning to appear more frequently than usual:

• Windows security updates (e.g., KB5066835) may tighten preview restrictions and block more files.
• Files downloaded from the internet are tagged with MOTW, triggering security checks.
• Group Policy or registry settings may prevent previewing untrusted files.
• Network locations not marked as trusted can block previews.
• Corrupted file metadata can confuse Windows security filters.
• Antivirus or security tools may interfere with preview functionality.

This explains why the issue often appears suddenly after updates or when accessing shared files.

Part 3. Fastest Fix: Unblock a Single File

Before trying advanced solutions, you can quickly unblock a file to restore preview functionality. This works because it removes the security flag attached to the file.

Steps to Unblock a File to Remove the Warnings on Windows

• Right-click the file that shows the warning and select “Properties”.

• In the “General” tab, look for the “Security” section and check the box labeled “Unblock” next to a message like “This file came from another computer and might be blocked”.

  

• Click “Apply” and then “OK” to save changes and unblock your file.

After this, reopen File Explorer and preview the file again.

Part 4. How to Fix “The File You Are Attempting to Preview Could Harm Your Computer” Permanently

If the issue keeps happening, you’ll need a more permanent solution. Below are the most effective methods.

Method 1. Bulk Unblock All Files with PowerShell

If you are dealing with multiple files showing the same warning, unblocking them one by one can be time-consuming. Using PowerShell allows you to remove the security flag (MOTW) from all files in a folder at once, giving you the file you are attempting to preview and fix. This method is ideal for users handling large batches of downloaded or shared files.

• Search for “PowerShell" and right-click to choose "Run as Admin."

• Run the command: “Get-ChildItem " C:\Users\YourUsername\Downloads " -Recurse | Unblock-File"

  

• Wait for the process to complete.

This removes security flags from all files in the selected folder.

Method 2. Disable MOTW for New Files via Group Policy

If the warning keeps appearing on newly downloaded files, it means Windows is automatically tagging them with security metadata. Disabling MOTW prevents this tag from being applied in the future. This helps stop the issue from recurring without affecting your existing files.

• Press “Win + R” then type “gpedit.msc” to open Group Policy Editor.

• Navigate to “User Configuration" > “Administrative Templates" > "Windows Components” > “Attachment Manager”.

• Find “Do not preserve zone information in file attachments” and set it to “Enabled," then click "Apply" and "OK" to save.

  

Now, new downloads won’t carry MOTW restrictions.

Method 3. Allow Preview for MOTW Files via Registry (with Caution)

Sometimes you may still want Windows security features enabled, but need preview functionality to work. This method allows previewing files even if they carry MOTW flags. It’s a more flexible solution, but it should be used carefully since it slightly reduces system protection when you are wondering why your preview pane is saying the file you are attempting to preview could harm your computer.

• Press Win + R, type “regedit” to open Registry Editor.

• Navigate to: “HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies”. If “Attachments” is available, skip to step 4; otherwise, create with steps 2 and 3.

• Right-click “Policies key” and select “New” then “Key” and name it "Attachments."

• Now, select “Attachments key” and right-click on empty space to select “New” and then “DWORD (32-bit) Value then name it “SaveZoneInformation."

  

• Double-click “SaveZoneInformation” and here you need to set “Value data” to “1”.

• Click “OK” then restart your computer.

Use this method carefully, as it reduces security restrictions.

Method 4. Compress the File to ZIP and Extract It

If you prefer a quick workaround without changing system settings, compressing and extracting the file can help. This process often removes the security metadata automatically. It’s a simple trick that works well for individual files.

• Right-click the file and choose “Send to," then click "Compressed (zipped) folder."

• Extract the ZIP file by right-clicking it and choosing "Extract All," then open the extracted file.

The new file often won’t carry the MOTW flag.

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Method 5. Uninstall Problematic Windows Update (KB5066835)

If the issue started suddenly after a system update, the update itself may be the cause. Certain updates, like KB5066835, introduce stricter security policies that block file previews. Removing the update can restore previous behavior and fix the issue.

• Go to “Settings” then “Windows Update," and click “Update History."

• Click “Uninstall updates” and locate “KB5066835," then click “Uninstall” against it and restart your PC.

  

This may restore normal preview behavior.

Method 6. Add Network Location to Trusted Zone

Files stored on shared drives or network locations are often flagged as untrusted by Windows. Adding these locations to the trusted zone tells the system they are safe. This allows previews to work normally without constant warnings.

• Open “Control Panel” > “Internet Options” and choose “Security tab”.

• Select "Trusted Sites" (or “Local intranet”) and click "Sites".

• Then in the pop-up panel, add the address of the network location, for example: [file://192.168.1.100/SharedFolder](file://192.168.1.100/SharedFolder).

• If you are adding non-HTTPS addresses, you need to uncheck the box against "Require Server Verification”.

  

• Apply changes and restart your computer.

Method 7. Turn Off Open File Security Warning (With Caution)

If none of the other solutions work, you can disable the warning entirely. This removes the restriction but also lowers your system’s security level. It should only be used when the preview pane is not working, and you are confident that all your files come from trusted sources.

• Click “Start” and search for “inetcpl.cpl” then press “Enter”.

• Now, go to the “Security” tab and click “Custom Level” to locate “Launching applications and unsafe files” and set this option to “Enable”.

  

• Save these changes and restart the PC.

Only use this if you fully trust your files.

⚡ Part 5. What If the File Still Can’t Be Previewed or Opened?

If none of the fix’s work, the file itself may be corrupted. In this case, simply removing security restrictions won’t help because the preview pane cannot process damaged data properly.

This is where a professional repair tool becomes essential. 4DDiG File Repair provides a reliable way to fix corrupted files, including documents, videos, and images. It is designed for both beginners and professionals, offering a high success rate when dealing with preview errors, file corruption, and unreadable formats.

Steps to Fix Corrupted Files with 4DDiG File Repair

• Install and open 4DDiG File Repair. Click “File Repair” then click “Add Files” to add your corrupted files.

  

• Click the “Repair All” button after adding all your corrupted files to fix them.

  

• Once the files are repaired, you can click "Preview" to check the results and "Save" to save the repaired file to your PC.

  

Once repaired, the file should open and preview normally without triggering errors.

FAQs

Q1: How do I turn off the open file security warning?

You can disable it through Internet Options by adjusting security settings under Custom Level. However, this reduces protection, so it’s best used only when working with trusted files or controlled environments.

Q2: How do I get rid of selecting a file to preview?

Ensure the Preview Pane is enabled in File Explorer and that the file is not blocked by security settings. If needed, unblock the file or adjust MOTW-related policies to restore normal preview behavior.

Q3: Could Windows file Preview harm your computer?

No, the preview itself does not harm your system. The warning exists because the file may contain unsafe content, so Windows blocks previewing it until you confirm it is safe.

Q4: Why did this warning suddenly appear after a Windows update?

Updates like KB5066835 can introduce stricter security rules, causing more files to be flagged. This is why previously safe files may suddenly show preview warnings.

Q5: How do I fix "the file you are attempting to preview could harm PDF" for PDF files specifically?

Unblock the PDF file via Properties or remove MOTW using PowerShell. If the issue persists, repair the file using a tool like 4DDiG File Repair to fix corruption issues.

Conclusion

The error about “the file you are attempting to preview could harm your computer ” is usually caused by Windows security features like MOTW rather than actual malware. By unblocking files, adjusting settings, or removing problematic updates, you can restore preview functionality quickly.

If the issue is caused by file corruption, 4DDiG File Repair offers a reliable solution to repair and recover files safely. With the right approach, you can fix preview errors and use your files without interruptions.