Your File Explorer Preview pane in Windows 11 is blank, or it shows “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.” If you see that warning, it’s usually not a sign that your PC is broken or infected: starting with Windows security updates released on and after October 14, 2025, Windows blocks previews of downloaded files on purpose (Microsoft Support, KB 5070960).
Quick Diagnosis: Which Problem Do You Have?
- The pane shows the “could harm your computer” warning. This is the October 2025 security change. Go to Fix #2.
- There’s no Preview pane at all. It’s turned off. Go to Fix #1.
- The pane is there but blank for every file. Check Folder Options (Fix #3), then restart File Explorer (Fix #4).
- Only PDFs or Word/Excel files won’t preview. The app’s preview handler is the likely problem (Fix #6).
- Only OneDrive files won’t preview. The file may be online-only (Fix #5).
- Only files on an office network drive won’t preview. Windows may treat that share as an internet location (Fix #2 and the network section below).
Why This Started Happening: The October 2025 Security Update
Windows tags files you download from the internet with a hidden flag called the Mark of the Web. Files opened from a network share that Windows classifies as part of the Internet zone get the same treatment.
Starting with Windows security updates released on and after October 14, 2025, File Explorer no longer previews files that carry this flag. It shows the warning above instead (Microsoft Support). Microsoft made the change to help prevent a vulnerability: a malicious file containing HTML tags that point to an external path could leak your NTLM credential hash (a scrambled form of your Windows login) to an attacker just by being previewed.
For Windows 11 versions 22H2 and 23H2, this change arrived in KB5066793. Other Windows 11 versions got it in their own October 14, 2025 or later updates. To see what’s installed on your PC, check Settings > Windows Update > Update history.
Don’t turn the protection off. Don’t disable Mark of the Web handling globally, change Internet zone settings, or apply registry hacks to bring previews back. Any of those reopens the credential-leak hole for every file you download. Unblock files one at a time instead, and only files you trust.
Common Issues and Solutions
Fix #1: Turn On the Preview Pane
Symptoms: No preview column on the right side of File Explorer.
Why it happens: The pane is off. Many File Explorer layouts hide it by default.
- Open File Explorer with
Win + E. - Select View in the toolbar.
- Select Show > Preview pane. On some builds, Preview pane appears directly under View.
- Select a file and check the right side of the window.
The Preview pane and the Details pane can’t be open at the same time. If you see file details instead of a preview, turn off Details pane under View > Show. You can also toggle the Preview pane quickly with Alt + P.
Verify: Select a plain .txt file or a photo you created on this PC. If it previews, the pane is working.
Fix #2: Unblock a File You Trust
Symptoms: The pane shows “The file you are attempting to preview could harm your computer.” The warning appears mostly on downloaded files, email attachments, or files from a network share.
Why it happens: The file carries the Mark of the Web, and the October 2025 update blocks its preview.
Only do this for a file you expected, from a sender or site you recognize, such as your own bank statement or a report a coworker said they’d send. If the file was a surprise, don’t unblock it. Open it with caution, or delete it.
- Right-click the file and select Properties.
- Stay on the General tab.
- Near the bottom, under Security, check Unblock.
- Select Apply, then OK.
- If the preview still doesn’t show, sign out of Windows and sign back in (Microsoft Support).
If you don’t see an Unblock checkbox, the file doesn’t carry the Mark of the Web. Your problem is something else, so continue with Fix #3.
Verify: Select the file again. Its contents should now appear in the pane.
About “Preview anyway”: Some reports suggest Microsoft may be testing a Preview anyway option in certain Windows builds (Windows Latest). Microsoft hasn’t confirmed this feature for general Windows 11 releases, so don’t count on seeing it yet.
Fix #3: Enable Preview Handlers in Folder Options
Symptoms: The pane opens, but it stays blank or shows only a large icon for documents.
Why it happens: Either Show preview handlers in preview pane is off, or Always show icons, never thumbnails is on.
- In File Explorer, select See more (the
···button) > Options. - Open the View tab.
- Under Advanced settings, check Show preview handlers in preview pane.
- Uncheck Always show icons, never thumbnails.
- Select Apply, then OK.
- Restart File Explorer (Fix #4) so the change takes effect.
Verify: Select a document you created on this PC. Content should appear in the pane instead of an icon.
Fix #4: Restart File Explorer
Symptoms: The preview worked before, then stopped without any obvious change. It often happens after an update or after the PC has been running a long time.
Why it happens: The File Explorer process (explorer.exe) is stuck or glitched.
- Press
Ctrl + Shift + Escto open Task Manager. - On the Processes page, select Windows Explorer.
- Select Restart task at the top.
- Your taskbar and desktop will briefly disappear and come back. Reopen File Explorer.
Verify: Open the folder again and test the preview. If File Explorer freezes or closes on its own while you do this, the problem is bigger than the Preview pane and needs separate troubleshooting.
Fix #5: Download OneDrive Files to Your PC
Symptoms: Local files preview fine, but OneDrive files show nothing. These files usually have a cloud icon in the Status column.
Why it happens: The file may be online-only, so its contents aren’t on your PC for File Explorer to preview. That’s a common cause, but not the only one: a OneDrive file can also be blocked by the Mark of the Web (Fix #2) or by a preview handler problem (Fix #6).
- Right-click the file or folder.
- Select Always keep on this device.
- Wait for the status icon to change to a solid green check mark.
- Select the file again.
Verify: The preview usually loads once syncing finishes. If it doesn’t, try Fix #2 and Fix #6. Online-only files open fine when double-clicked, so this problem can be easy to miss.
Fix #6: Repair the PDF or Office Preview Handler
Symptoms: The pane is on and Fix #3 is done, but PDFs or Word, Excel, or PowerPoint files still show blank. Other file types preview fine.
Why it happens: Apps install small components called preview handlers that let File Explorer draw their file types. If a handler is missing, disabled, or corrupted, that file type won’t preview.
For Office files (Word, Excel, PowerPoint)
- Close all Office apps.
- Go to Settings > Apps > Installed apps.
- Find Microsoft 365 (or your Office version) and select the
···menu next to it. - Select Modify, then approve the User Account Control prompt.
- Choose Quick Repair and select Repair.
- Restart your PC when it finishes.
If Quick Repair doesn’t help, run it again and choose Online Repair. It takes longer and needs an internet connection.
If Office isn’t installed at all, Word and Excel files may not preview unless another app on your PC registers a preview handler for those formats. Installing the Office desktop apps is one way to add those handlers, but you don’t need it if another installed app already provides them.
For PDF files
- Open your PDF reader’s settings or preferences.
- Look for an option about previews or thumbnails in Windows Explorer, and turn it on if it’s off. The wording differs between apps.
- If there’s no such option, try updating or reinstalling the PDF reader so it re-registers its preview handler.
- Restart File Explorer (Fix #4).
Verify: Select a PDF or Office file you created on this PC, not a downloaded one. A downloaded file may still be blocked by the Mark of the Web, which Fix #2 handles.
Fix #7: Install Pending Windows Updates
Symptoms: The preview broke right after an update, or Windows has been nagging you to restart.
Why it happens: A half-installed update can leave File Explorer components out of sync.
- Go to Settings > Windows Update.
- Select Check for updates.
- Install everything offered.
- Restart your PC, even if Windows doesn’t ask you to.
Verify: Test the preview on a file you created locally. Downloaded files will still show the security warning after updating, because that behavior is intentional.
Fix #8: Run SFC and DISM
Symptoms: Previews fail for many file types, and Fixes #1–#7 haven’t helped.
Why it happens: Corrupted Windows system files are affecting File Explorer components.
Before you run repair tools on a PC that’s acting up, back up important files to an external hard drive or OneDrive.
- Right-click Start and select Terminal (Admin). Approve the prompt.
- Run
sfc /scannowand wait for it to reach 100%.
- If SFC reports that it found corrupt files it couldn’t fix, run
DISM /Online /Cleanup-Image /RestoreHealth. - When DISM finishes, run
sfc /scannowonce more. - Restart your PC.
Verify: Test the Preview pane with local files of several types.
Error Messages and Symptoms Quick Reference
| What you see | What it means | Fix |
|---|---|---|
| “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.” | The file has the Mark of the Web, and the October 2025 update blocks its preview | Fix #2 (trusted files only) |
| No Preview pane at all | The pane is turned off | Fix #1 |
| File details shown instead of a preview | The Details pane is on instead | Fix #1 |
| Blank pane or a large icon only | Preview handlers are off, or icons-only mode is on | Fix #3 |
| Only PDFs or Office files are blank | The app’s preview handler is missing or broken | Fix #6 |
| OneDrive files blank, local files fine | The file is online-only | Fix #5 |
| Network share files show the warning | The share is treated as an internet location | Fix #2, then ask your IT admin |
| Everything is blank after an update | Stuck Explorer or a pending update | Fix #4, then Fix #7 |
Network Drives and Work PCs
Office file shares are a common trigger for the warning. If Windows treats your file server as part of the Internet zone, every file on it gets the Mark of the Web treatment. Even trusted internal files won’t preview (Microsoft Learn Q&A).
For a few files, unblock them one at a time with Fix #2. For the whole share, ask whoever manages your network to confirm how the server should be classified. An administrator who has assessed the share can add it to the Local intranet or Trusted sites zone. Don’t change zone settings yourself to make the warning go away. That relaxes security for everything coming from that location.
On company-managed PCs, an administrator policy can also stop you from turning the Preview or Details pane on or off. If the toggle in Fix #1 does nothing, ask IT before troubleshooting further.
Configuration Mistakes to Avoid
- Turning on the Details pane and expecting a preview. Only one of the two panes can be open at a time. Use View > Show > Preview pane.
- Leaving icons-only mode on to speed things up. Always show icons, never thumbnails also hides document previews. If File Explorer feels sluggish, troubleshoot the slowdown separately instead of disabling thumbnails.
- Unblocking a whole folder of downloads at once. Check each file. Unblocking is a trust decision, not a cleanup step.
- Using registry or zone “fixes” from forums. These remove the protection instead of fixing anything.
Getting Help
If you need to post on a forum or contact support, collect this information first:
- Windows version and build: Settings > System > About
- Installed updates: Settings > Windows Update > Update history
- SFC log:
C:\Windows\Logs\CBS\CBS.log - DISM log:
C:\Windows\Logs\DISM\dism.log - File details: the file type, where it came from, and whether its Properties dialog shows an Unblock checkbox
Microsoft’s Q&A forum has active threads on this exact problem, including Preview pane suddenly stopped working and how to fix “the file you are attempting to preview”. If search inside File Explorer is also broken, that’s a separate issue covered in HDG’s Windows Search fix guide.
Prevention Tips
- Keep Windows updated. Security fixes and File Explorer fixes arrive through Settings > Windows Update.
- Save trusted work files from a known source. For example, sync files from your company’s OneDrive or SharePoint rather than downloading them through a browser. Files you create yourself don’t carry the Mark of the Web.
- Treat the warning as a speed bump, not an obstacle. It’s a good moment to ask whether you really expected the file.
- Keep Office and your PDF reader updated so their preview handlers stay registered.
Frequently Asked Questions
What does “the file you are attempting to preview could harm your computer” mean?
The file came from the internet or from a location Windows treats as the internet. Since the October 14, 2025 security updates, Windows blocks previews of these files to prevent credential leaks (KB 5070960).
Is my PC infected, or is this a Windows bug?
Usually neither. It’s an intentional security feature, and the message alone isn’t a sign of malware. If you also see other problems, such as crashes or unexpected pop-ups, run a malware scan to be safe.
Is it safe to click Unblock?
Yes, if you expected the file and trust where it came from. Don’t unblock files from unknown senders or files you weren’t expecting.
Why did this start happening recently?
The behavior arrived with Windows security updates released on and after October 14, 2025. That’s why the problem seemed to appear overnight.
Why won’t my PDF or Word document preview even though the pane is on?
If there’s no warning message, the app’s preview handler is usually missing or broken, or preview handlers are disabled. Try Fix #3, then Fix #6.
What if nothing works?
Run SFC and DISM (Fix #8). If previews still fail across all file types, an in-place repair of Windows from Microsoft’s site is the next step.
Wrapping Up
If you’re seeing the “could harm your computer” message, Fix #2 is the real answer: unblock the files you trust and leave the rest alone. The warning is Windows protecting you, so don’t hunt for a hack to remove it.
For a plain blank pane, start with Fix #3 (Folder Options) followed by Fix #4 (restart File Explorer). If SFC keeps finding corruption, or Explorer crashes while you troubleshoot, run a full malware scan and back up your important files before going further.
| Step | Action | Applies To |
|---|---|---|
| Fix #1 | Turn on the Preview pane | No pane visible |
| Fix #2 | Unblock trusted files | “Could harm your computer” warning |
| Fix #3 | Enable preview handlers, disable icons-only mode | Blank pane |
| Fix #4 | Restart Windows Explorer | Sudden failure |
| Fix #5 | Always keep on this device | OneDrive files |
| Fix #6 | Office Quick Repair or PDF reader settings | PDF and Office files only |
| Fix #7 | Install pending updates | Broke after an update |
| Fix #8 | SFC and DISM | Nothing else worked |
Last updated to reflect the October 2025 File Explorer security change | Applies to File Explorer on Windows 11 (all supported editions)