If you’re unable to preview PDFs in Windows 11 File Explorer and see a warning saying “The file you are attempting to preview could harm your computer,” don’t worry — you’re not alone. This issue started appearing after the October 2025 security update (KB506835), and it’s affecting many users trying to open or preview PDFs in folders like Downloads, Documents, or Desktop.

In this detailed guide, we’ll walk through two reliable methods to fix the issue — one using PowerShell and another using the Registry Editor. Both are safe when performed carefully, and we’ll explain each step clearly along with why it works.

Let’s start by understanding what’s actually causing this problem before moving to the fixes.

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1. Understanding the PDF Preview Error in Windows 11

When you select a PDF in File Explorer, the right-hand preview pane normally shows its contents without opening the file. But after the October 2025 update, some users began seeing this error message instead:

“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.”

This warning prevents you from previewing PDFs directly, even if the file is completely safe. It’s particularly frustrating for professionals who rely on File Explorer previews for quickly checking invoices, documents, or downloaded PDFs.

So, what’s really happening here?

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2. Why Does This Warning Appear After KB506835?

The root cause is a bug introduced in Windows 11 update KB506835, released as part of the October 2025 security patch.

Microsoft’s goal was to improve file safety in File Explorer by adding stricter preview sandboxing. Unfortunately, this update unintentionally flags PDF preview handlers (used by Edge or Adobe Acrobat) as “potentially unsafe.”

So, even legitimate PDFs stored on your computer trigger this message. Until Microsoft issues a permanent patch, users can apply a workaround that safely re-enables PDF previewing.

Let’s begin with the first and easiest fix using PowerShell.

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3. Fix 1: Unblock PDF Files Using PowerShell

If you only want to fix the issue for specific folders (like Downloads or Documents), PowerShell is the safest way. This command removes the “blocked” security attribute from PDFs in the selected directory.

Before we dive into the steps, make sure you’re logged in as an administrator.

Step-by-Step Instructions

Let’s move to the detailed part:

1. Open PowerShell as Administrator
   • Click on the Start button or use the Search bar.
   • Type PowerShell.
   • Right-click on Windows PowerShell and choose Run as administrator.
2. Type or Paste the Following Command
   In the PowerShell window, enter the command below. Replace Admin with your Windows username and Downloads (or whichever folder contains the PDF). Get-ChildItem "C:\Users\Admin\Downloads\*.pdf" | Unblock-File This command finds all PDF files in that folder and unblocks them for preview.
3. Press Enter to execute the command. You’ll see no confirmation message — PowerShell will simply process the command silently.
4. Check the File Explorer Preview
   • Open File Explorer.
   • Go to the folder where your PDF is saved.
   • Select the file and enable the Preview Pane (shortcut: Alt + P).
   • You should now be able to see the PDF preview correctly.
5. Close PowerShell once you’ve verified the fix.

💡 How it works:
The PowerShell Unblock-File command removes the “Zone.Identifier” data (metadata Windows attaches to files downloaded from the Internet). This data was triggering the overprotective warning after the update.

If this method doesn’t resolve the issue globally or if you want to permanently disable preview restrictions, move on to the next solution.

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4. Fix 2: Disable File Explorer’s Built-In Preview Security Using Registry Editor

Now, let’s look at a more permanent and system-wide method. This one disables the extra file safety check that File Explorer performs before showing previews.

If you’re confident about the safety of your files, this fix restores normal preview behavior for all users on your computer.

⚠️ Important Before You Proceed

Editing the Registry can affect system behavior if done incorrectly. Always create a backup or system restore point before proceeding.

Here’s how you can safely do it:

Step-by-Step Guide

1. Open the Registry Editor
   • Press Windows + R to open the Run dialog.
   • Type regedit and hit Enter.
   • If prompted by UAC, click Yes.
2. Navigate to the Following Path: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies
3. Create a New Key
   • Right-click the Policies folder.
   • Choose New → Key.
   • Name the new key: Attachments
4. Add a New DWORD (32-bit) Value
   • With the new Attachments key selected, right-click on the right pane.
   • Choose New → DWORD (32-bit) Value.
   • Name it: SaveZoneInformation
5. Modify Its Value
   • Double-click SaveZoneInformation.
   • Change the Value data from 0 to 1.
   • Click OK to save changes.
6. Close the Registry Editor and Restart Your PC.

Once restarted, open File Explorer and select a PDF file — you should now see the full preview without warnings.

🧠 What This Does:
This registry tweak disables Windows from attaching “Zone Information” metadata to files. Essentially, Windows stops flagging local or downloaded files as suspicious for previewing.

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5. Important Notes & Warnings

Let’s pause for a moment and go through some essential precautions and clarifications.

• This fix removes a layer of file safety, so use it only if you’re confident your files are from trusted sources.
• Always keep your antivirus enabled (like Microsoft Defender) — this registry edit doesn’t disable your main protection.
• If you use corporate or school accounts, check with your IT administrator before applying registry changes.
• Microsoft is expected to release a fix in a future cumulative update, so you can revert these changes once that patch arrives.

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6. Frequently Asked Questions

Q1. Will disabling this security setting make my PC unsafe?
Not necessarily. It only affects how File Explorer handles file previews — your antivirus and Windows SmartScreen will still protect you.

Q2. Can I revert these changes later?
Yes. Simply go back to the same registry location and delete the SaveZoneInformation entry or set its value to 0.

Q3. Is there any tool to do this automatically?
You can achieve the same result using a .reg file, but it’s safer to follow manual steps unless you trust the source completely.

Q4. Why didn’t Microsoft fix it yet?
This issue was newly introduced with the October 2025 patch (KB506835). A fix may come in the next cumulative update after internal testing.

Q5. Do I need to reinstall Adobe Acrobat or Edge PDF viewer?
No. The issue isn’t caused by your PDF viewer — it’s a Windows File Explorer bug.

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7. Final Thoughts

While the October 2025 security update improved overall system safety, it also introduced an annoying PDF preview issue for many users. Thankfully, the methods outlined above provide safe and practical workarounds until Microsoft releases an official fix.

If you often preview PDFs or images through File Explorer, the PowerShell method is safer for single folders, while the Registry method is better for global correction.

Once Microsoft pushes the next update, you can undo these tweaks to restore default protection settings.

Until then, your PDF previews in Windows 11 should work perfectly again.

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Disclaimer:
Editing system registry settings should always be done with caution. The steps shared here are based on verified troubleshooting methods from trusted technical sources. Proceed carefully and always ensure your system is backed up.

For official updates and release notes, visit Microsoft’s Windows Update page.

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#Windows11 #PDFPreviewError #PowerShellFix #RegistryEditor #WindowsUpdate #FileExplorer

Emily Carter

Emily is a Windows power user and technical writer from the UK. She has spent 7+ years in IT consulting, helping businesses migrate to new Windows versions, optimize performance, and solve common errors. Emily’s articles combine professional experience with step-by-step clarity, making even registry hacks accessible to everyday users.

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