File Explorer not previewing pdf files since 25H2 update

Same issue here after running 10/15/25 update. getting same message on 99% of the files, Word, PDF, Excel, etc. Tried uninstalling/rolling back the update and ran into another error. 0x800f0825... 10/16/25 - emailed MS support regarding update uninstall error... and MS support basically went Goodfellas on me.. F U pay me. I have to now choose to pay for a support plan.

funny how this is coming up right as they end Win10 support. Unreal!

I'm suffering from this too! I cannot understand why a simple update would disable the ability to preview files, which we've enjoyed for years. This is now crippling my daily work, and driving me crazy.

Hi,

Thanks for checking those already, and good call on trying the repair too.

Regards,

This is extremely frustrating and time wasting as we use the preview pane for all our pdf files. Opening each file to view it is an extreme time waster for us. Please Microsoft, give us an easy fix.

I uninstalled and no change :( ---UPDATE: Uninstalled all updates that came with the 25H2 updates on 10/15/25. Restarted and all was good. The updates re-installed overnight. Uninstalled again and turned off automatic updates. So far all good.

I uninstalled the update (which was installed for me on the 15/10) and it works great now. I can preview the files just fine.

My other colleagues - who were also struggling with this update - have tried the uninstall method and it has worked. It may not work for all, but it should work for most.

Just add the path where your files are saved.

1. Go to Internet Options.
2. Go to Security Tab.
3. Go to Trusted sites and click sites.
4. Add the path where your files are saved. Make sure you uncheck the "Require server verification (https:) for all sites in this zone.
5. All done, go ahead and try if it works.

This only works for internet sites with a https:// prefix. I don't believe you can add local or network drives here...

Well done, Masha Allah, it works, thank you brother.

Paul Nicholson it works for me. If you type file://then your path.

my example is file://desktop-2022\users\ME\Desktop\Email attachments to rename\

I was having the same issue with a customer of ours,

Their issue was when the PDF files are located in their OneDrive folder on file explorer.

If anyone is having issues with it just being PDF previews inside the OneDrive folder, what you can do is this:

1. Open Control Panel
2. Search for Internet Options
3. Open the Security tab
4. Click on Trusted Sites
5. Then press the "Sites" button
6. Then finally, add "www.onedrive.com" into the trusted sites page.

For PDFs on physical drives, it doesn't look like there is no permanent fix, but theres an answer on this forum relating to power-shell that looks like it works.

Yup, similar issue with the latest update. Image files seem to appear in the preview pane, but 3d files don't show in file explorer's preview pane anymore as well as some pdf files. Note I added 3dview for Win 11 home, which worked fine until the update. Curiously zipped files with 3d files etc show fine in the preview pane when accessed.

I was getting hopeful with a couple of the suggestions.

My files are actually on a shared Teams folder synched to my OneDrive, so added both www.onedrive.com and the Teams Sharepoint path to Trusted Sites on Internet Settings.

Also added the file path as per Drewstein's suggestion in this form:

file://desktop-2022\users\ME\Desktop\Email attachments to rename\ (obvs changed for my path)

Unfortunately none of them have worked for me...😖

Does this mean we need to ignore update from now on?

Could this mean a switch to apple?

What a pain!

I've tried the different "fixes" as well and it's nothing is working for me either. Word, Excel, and images preview - PDFs and TEXT files are NOT. This is the same issue with both local locations (i.e. on my hard drive) and on cloud based paths.

Apple has its own version of this, since there are RAMPANT issues with security these days. The entire concept of "getting things from outside your desktop" is a problem that needs to be addressed by all major players. Do not ignore updates, it's actually quite the opposite. Ensure you ARE updated.

I also UN-installed ... An hour of my life I'll never get back!

My question is, if my PC is on Auto Update, then the same issue will come up again, correct? I've never had a problem with Windows updates until today. I'd rather keep my PC up to date!

I resolved this at my company. You need to put "file://" in front of any area you are trying to allow. Follow the instructions Crsjn describes but add "file://"

This worked like a "hot damn"! Thanks everyone!!

Cool, Microsoft deploys new "security features" with no way to manage them apart from a hacky and all out "disable security feature". Seems MS hasn't learned anything and I will continue to be baffled by their approach to anything but data mining and greed.

Hello.

I have today noticed this message & I have not yet downloaded/installed 25H2.

It was discovered the Security Update for Microsoft Windows (KB5066835), installed on Oct 15, 2025 could be the culprit. I uninstalled the update & previewing .pdf's has been restored.

I hope this helps.

Has anyone found a permanent solution so far, or do we need to wait for a new Microsoft update to resolve this issue?

1. Go to Internet Options.
2. Go to Security Tab.
3. Go to Local Intranet
4. Klik Advanced
5. add Ip Address if file from share network
6. Apply

Adding our Shared Drive (t:) with the file:// seems to have sorted the issue. This was happening on a 24H2 and a 25H2 system, so I don't believe that it's entirely a 25H2 issue.

I have not yet installed the update but am getting the same message on my computer when I try to open PDF that are stored in my downloads. This is most inconvenient as I preview everything before I open it. Why is this happening since I haven't even installed the update yet>

I use the preview option daily and this is causing me to spend more time opening and closing documents (especially pdf files). This is not good and Microsoft needs to fix it immediately. This is not a safety issue for me since I'm usually on a closed network and wouldn't open a file I'm not familiar with anyway.

Hear US Microsoft!!!! Turn this safety feature off in your next update since you are having them several times a week lately. Make it optional if someone needs it. Don't force it on all of us. I've tried clicking the unblock box on a pdf file and it still didn't work. I have thousands of files and can't spend the time to do this for everyone I need to access all day almost everyday.

Just uninstall this update: KB5066835 and it will work again.

I am having the same issues on Windows 10 and Windows 11

check my answer.

Is the removal of preview for documents with the mark of the web a mitigation for the rendershock exploit?

Hi! I just got the solution, just download the expernal file manager, ONE COMMANDER and it’s way much much better!! And it does preview pdfs but not ms office files though

Solution 1: Registry Edit (Recommended)

This procedure will configure Windows not to save zone information (Mark of the Web) for new file attachments.

⚠️ Warning: Editing the Registry incorrectly can cause system errors. Proceed with caution.

Press Win + R to open the Run dialog box.

Type regedit and press Enter. Click Yes if the User Account Control window appears.

Navigate to the following key in the Registry Editor:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies

Create a New Key:

Right-click on the Policies key, select New -> Key.

  Name the new key __`Attachments`__.
  
  __Create a New DWORD Value:__
  
     Right-click on the newly created __`Attachments`__ key, select __New__ -> __DWORD (32-bit) Value__.
     
        Name the new value __`SaveZoneInformation`__.
        
        __Modify the Value:__
        
           Double-click on __`SaveZoneInformation`__.
           
              Ensure the __`Value data`__ is set to __`1`__.
              
                 Click __OK__.
                 
                 __Close the Registry Editor__ and __Restart your computer__ to apply the changes.
                 

After restarting, new PDF files downloaded or created should no longer trigger the preview error.

Solution 2: Disable via Group Policy Editor (Applies to Windows Pro/Enterprise only)

If you are using Windows Pro or Enterprise edition, you can achieve the same result through the Local Group Policy Editor:

Press Win + R, type gpedit.msc and press Enter.

Navigate to:

User Configuration
-> Administrative Templates
-> Windows Components
-> Attachment Manager

Find the setting "Do not preserve zone information in file attachments".

Double-click this setting and select Enabled.

1. Click Apply and OK.

Restart your computer to apply the changes.

Solution 1: Registry Edit (Recommended)

This procedure will configure Windows not to save zone information (Mark of the Web) for new file attachments.

⚠️ Warning: Editing the Registry incorrectly can cause system errors. Proceed with caution.

Press Win + R to open the Run dialog box.

  Type __`regedit`__ and press __Enter__. Click __Yes__ if the User Account Control window appears.
  
     Navigate to the following key in the Registry Editor:
     
     ```
     HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies
     ```
     
        __Create a New Key:__
        
              Right-click on the __`Policies`__ key, select __New__ -> __Key__.
              
                    Name the new key __`Attachments`__.
                    
                       __Create a New DWORD Value:__
                       
                             Right-click on the newly created __`Attachments`__ key, select __New__ -> __DWORD (32-bit) Value__.
                             
                                   Name the new value __`SaveZoneInformation`__.
                                   
                                      __Modify the Value:__
                                      
                                            Double-click on __`SaveZoneInformation`__.
                                            
                                                  Ensure the __`Value data`__ is set to __`1`__.
                                                  
                                                        Click __OK__.
                                                        
                                                           __Close the Registry Editor__ and __Restart your computer__ to apply the changes.
                                                           
                                                           After restarting, new PDF files downloaded or created should no longer trigger the preview error.
                                                           
                                                           Solution 2: Disable via Group Policy Editor (Applies to Windows Pro/Enterprise only)
                                                           
                                                           If you are using Windows __Pro__ or __Enterprise__ edition, you can achieve the same result through the Local Group Policy Editor:
                                                           
                                                              Press __Win + R__, type __`gpedit.msc`__ and press __Enter__.
                                                              
                                                                 Navigate to:
                                                                 
                                                                 ```
                                                                 User Configuration

-> Administrative Templates -> Windows Components -> Attachment Manager ```

                                                                    Find the setting __"Do not preserve zone information in file attachments"__.
                                                                    
                                                                       Double-click this setting and select __Enabled__.
                                                                       
                                                                          Click __Apply__ and __OK__.
                                                                          
                                                                             __Restart your computer__ to apply the changes.
                                                                             

If you install PowerToys and activate .pdf in File Explorer add-ons, then uncheck the above in folder options, it should work

While I was aware that Windows flagged downloaded files as unsafe I had never heard the term MoTW. Whoever slipped Mark of the Web into Microsoft's metadata lexicon is a real Beast.

I ran into the same problem after the update, so I checked this feed. I'm not super into tech stuff (I didn't understand how to go about one of the answers here) but I tried clicking "Print to PDF" option while viewing the received PDF files online. I then saved it on my PC folder, closed the folder and reopened to see if it worked. Well, it did. I think the print-to-save as PDF option is bypassing any security feature that has been installed, and the system reads it as your "own" file.

this worked for me (elevated ps), uninstalled recent update kb5066793, and restarted computer:

wusa /uninstall /kb:5066793

restart-computer

or also elevated ps, just recursively unblock a certain parent folder's pdf files (BUT, you'll have to redo that command with e.g. new downloads; but also note, you can just right click on any given file > properties, and at the bottom of the General tab, is the new security option, where you just check that "unblock" box):

gci c:\users\youHere\downloads -include *.pdf -recurse | unblock-file

I have the same problem and here is an interesting observation... Older pdf files dating from before about July 2022 preview without a problem.

use Alt+V+P at a time it enables preview pan

We have the same issue after the 25H2 Update.
After some troubleshooting we got around the issue by using the DNS (Server/Computer) name instead of the IP address. So instead \x.x.x.x\NetworkShare use \ServerName\NetworkShare instead. Hope this fixes the issue for you all as well.

I'm far from an expert, but the fix that @CrsJn provided above worked for me. I am now able to see previews of network files. The trick is to make sure you uncheck "Require server verification (https:)" before adding the local link. Then I just added file://**.myserver.mydomain
Can anyone comment as to if unchecking the Require server verification (https:) box adds much of a security risk?

Reverting to the previous install (not 25H2) reactivated the PDF display in Explorer. I figured that letting MS figure out the problem and fix it would be best. In the future I'll do a search to issues related to any upgrades before I initialize anything.

I've had the same problem and believe I've found a solution.

Open Adobe Acrobat

Go to menu

• Preferences
• Security (enhanced)
• Under 'Sandbox Protections'
  • UNcheck 'enable protect mode at startup'
• Under 'Enchanced Security'
  • UNcheck 'enable enhanced security'
• Select 'OK'

I hope this works for you.

Adding IPs to Internet Options - Trusted sites only works for files created by the same machine. Files received from others or downloaded from Internet are still getting blocked in the preview panel

Hi,

Adding the network location to the trusted locations as file:///Z:/... worked for me (you have to disable https requirement)

I rely on the Preview pane to scroll through literally hundreds of PFD drawings and other files to reference markups made. Suddenly I have to open those files individually, one by one, in a PDF viewer, and my workflow slows to a crawl. WTF????

Typically, selecting "Unblock" in the file properties will resolve the issue. However, if you need to process a large number of files, it is recommended to use the Streams tool provided in the link below. You will need to either search the instructions on how to use the stream tool and let AI guide you through it

https://v4.hkg1.meaqua.org/en-us/sysinternals/downloads/streams

This tool can be used to remove all "Mark of the Web" tags from your files. Doing so should resolve your issue. Additionally, please consult with your system administrator to prevent these tags from being automatically reapplied through Group Policy in the future.

If you add the file location to the trusted sites tab in internet options, this fixes the issue. Use file://[file location]

This can also be added as a group policy to apply to all the PCs across a domain.

I uninstalled 25H2 and Preview worked for 5 minutes - then stopped working again, even for PDF's that I created myself on that system. WTF??

I ran the command Unblock-File -Path "C:\Users\admin\Documents\*.pdf" in PowerShell, and it only temporarily resolved the issue. When the user saves new PDF files, the problem comes back again.

I would like to request Microsoft to provide a permanent fix for this issue as soon as possible.

Here is a simple solution that worked for me -

in the file explorer, just disable this check box as shown in the image, this simply worked for me

I tried this, but unless I missed something else, it turned off all of my previews, even the ones that I had "fixed" using the "unblock" trick that I described in a previous post.

You should try and check your "Trust Manager" within you Pdf Viewer / Software.
Once I edited or checked my settings, all was good and back to normal.

I also tried this - but it turned off ALL previewing of files (both local and on a network).

@Jeff N your suggestion worked for my system - none of the other suggestions (and I've been following this since Oct 16th) have worked for me.

Open Adobe Acrobat

Go to menu

• Preferences
• Security (enhanced)
• Under 'Sandbox Protections'
  • UNcheck 'enable protect mode at startup'
  • Under 'Enchanced Security'
    • UNcheck 'enable enhanced security'
    • Select 'OK'

UPDATE - Oct 24 - it worked until I restarted my laptop. Randomly, some PDFs are viewing, and others are still not. Wonky!

This is an INSANE situation. I am totally on board for all things security-oriented, but perhaps not this one which is so far-reaching. I am on a STANDALONE LAPTOP and NOT ON A NETWORK. I can't even guess how many PDF files I presently have. Yes, I can call up one document, go to properties, and unblock it. But, I can't select all of the PDF files in the folder and use properties to apply unblock to all of them. We'll be on 26H2 by the time I do them al one-by-one! I'm only managing personal files, so I can't imagine how people working remotely are able to overcome this disastrous change. I see there are some solutions in the comments below, so I will give them a try. But, we should not have to "apply a solution" each and every time a new PDF document shows up and is saved on a local drive. Isn't that why we already use Defender and/or other security software products?

I am not able to preview pdf files and everytime getting message - "The file you are attempting to preview could harm your computer." Please troubleshoot the problem

Below solution steps worked for me:

1. Check if you are missing PreviewHandlers Registry Key, if yes then use below:

Method 1) Fix: Recreate the Missing PreviewHandlers Registry Key

Step 1. Open Registry Editor

1. Press Win + R, type regedit, and press Enter.
   1. Navigate to:

            HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
      

   Step 2. Create the Missing Key
2. Right-click Explorer → New → Key.
   1. Name it exactly:

            PreviewHandlers
      

   Step 3. Restore Default Preview Handler Entries Inside PreviewHandlers, create the following String Values (REG_SZ) — you can copy and paste both the names and values exactly:

Name (Default Preview Handler)Value (CLSID)Microsoft Office Preview Handler{65235197-874B-4A07-BDC5-E65EA825B718}Microsoft Office Preview Handler{65235197-874B-4A07-BDC5-E65EA825B718}Microsoft PDF Preview Handler{DC6EFB56-9CFA-464D-8880-44885D7DC193}Microsoft Word Preview Handler{84F66100-FF7C-4fb4-B0C0-02CD7FB668FE}Microsoft Excel Preview Handler{00020827-0000-0000-C000-000000000046}Microsoft PowerPoint Preview Handler{65235197-874B-4A07-BDC5-E65EA825B718}Microsoft Outlook Mail Preview Handler{A776EDEF-81C0-4A3C-BE0A-46E36A9B8E2D}Text Preview Handler{1531d583-8375-4d3f-b5fb-d23bbd169f22}Image Preview Handler{FFE2A43C-56B9-4bf5-9A79-CC6D4285608A} (You don’t need all of them; adding the Text, PDF, and Image handlers is usually enough.)
It should look like below screenshot:

Step 4. Restart Explorer

Either reboot, or open Command Prompt and run:

   taskkill /f /im explorer.exe
start explorer.exe

Then test your preview pane again. If it did not work, then use below solution as well:

I also used Mark Zuber's suggestion and used below method:

Method 2)

Automate It for Multiple Common Folders

If you want this to apply to multiple folders, use a script like this:

$folders = @(
  "$env:USERPROFILE\Downloads",
  "$env:USERPROFILE\Documents",
  "$env:USERPROFILE\Desktop"
)

foreach ($folder in $folders) {
  if (Test-Path $folder) {
    Write-Host "Unblocking files in $folder..."
    Get-ChildItem -Path $folder -Recurse -ErrorAction SilentlyContinue | Unblock-File
  }
}
Write-Host "✅ All files have been unblocked successfully."

🔹 Save it as UnblockFiles.ps1, then run it once as Administrator (right-click → Run with PowerShell). This clears MOTW tags from typical folders where downloaded content lives.

I hope it will help everyone until Microsoft has a fix for it. The above may not be a proper solution, and may not work for everyone. But is a workaround for now and worked for me.

I am also having this same issue since the update and nothing has worked.  Oddly enough I can view pdfs created before the security update but not any 'newly created or downloaded' pdfs regardless of the files location. Beyond frustrating.  I have spend way too long trying every fix listed in this forum to date and nothing has worked.  We need a windows update to fix this - hello windows are you there?

J'ai le même problème mais sur Windows 10 ! Je pensais que cela venait d'Acrobat car quand je l'ai désinstallé et installé Fox It Reader à la place, mes aperçus fonctionnaient à nouveau jusqu'à ce que j'ai redémarré le PC. Depuis impossible de voir les aperçus PDF en grande taille. PAr contre Excel, Word et Jpeg fonctionnent.

So as a temporary solution for just 1 or 2 files at a time, I have had to right click on the file - go to Properties of the file and then unblock, but this is time consuming to do for every file

I am finding today that 3D object files, such as .obj now have the same warning and no preview even though I created them on this PC.

I have to believe at this stage its a bug.

Nope not a bug, this is by design - read this and weep its permanent behaviour, Microsnot has decided we need protecting from ourselves

https://support.microsoft.com/en-us/topic/october-14-2025-kb5066835-os-builds-26200-6899-and-26100-6899-1db237d8-9f3b-4218-9515-3e0a32729685

I have the same problem, and for now its FIXED. You can follow this step:

https://allthings.how/fix-file-explorers-pdf-preview-warning-in-windows-11-25h2/

Hi

This is what I received from Microsoft support regarding this issue:

This is one of the security measures applied after the October KB.

Given that authentication occurs when connecting to the remote path to ask what files exist on the target, the mere listing of files in a remote path implicitly leaks the NTLM hash to that remote path

The issue in the MSRC hardened on and after 10B.25 is that File Explorer doesn't ask a previewer to preview the contents of a downloaded file, because there’s currently no way for a previewer to convey it understands the risk of leaking NTLM hashes to remote locations and does NOT do so when previewing untrusted files.

This change addresses a security vulnerability (MSRC 98973) where NTLM hash leakage could occur when users preview unsecure files (e.g., HTML/JS) in File Explorer. The issue arises when HTML tags such as <link>, <src>, or similar attributes reference external paths, enabling attackers to exploit preview functionality. Only way is to unblock those files to remove the mark of web or copy them to a trusted folder.

Workarounds: Remove the internet security block by adding the file shares address to the Local intranet or Trusted sites security zone.

Right-click -> Properties -> Check “Unblock”.

This workaround is publicly documented under “How can I override or unblock this behavior?" in the Frequently Asked questions section of Public KB5070960: File Explorer automatically

If you are confident in the safety of both the file and its source, you may remove the internet security block.

To remove the block for a downloaded file, right-click the file in File Explorer, select Properties, and then select Unblock.

Note: The change might not take effect immediately but will be effective after the next login.

To remove the block for files on an Internet Zone file share, use the Internet Options control panel’s Security tab to add the file share’s address to either the Local intranet or Trusted sites security zone.

Warning: This configuration change will relax the security posture for all files from the listed file share.

Br

Dan

Same issue here. It is so incredibly frustrating that Microsoft sees fit to create these roadblocks for us which decrease efficiency, and then fail to address the issue. I've tried every recommended fix, but the damnable preview block always turns itself back on no matter what I do. It does NOT make sense to force cloud users like myself to open EVERY SINGLE FILE EVERY SINGLE TIME if I need to read it. MICROSOFT PLEASE CORRECT THIS.

I send the PDF files as attachment to myself and when I save the files from my mail, windows consider them to be trusted and they can be seen in preview.

So instead of fixing the security whole, they just removed the ability to preview files. This was unbelievable short-sighted.

Hi, any update?

this was the worst update they made, I keep rolling back. I need to preview items, at least allow an option where we know the risks. some of these documents are documents I have made

This deeply underthought error continues even from sites I have added to our 'Trusted Zone' - such as our cloud-based accounting and workflow applications. (Try finding one that isn't cloud-based these days.) 'Unblock'ing individual files also doesn't work, not immediately, not upon restarting Explorer, not even upon restarting the whole computer, and the option to Unblock is gone anyway once it's clicked once.
Our IT is managed outside our organisation, so I have no recourse for receiving updates or rolling them back. I cannot access PowerToys or PowerShell without their admin access.

Sack the dev team for this "security update".

So after running a script and waiting hours to unblock all of my files, only the preview pane was showing but the thumbnails were still the pdf icon. I googled "adobe thumbnail pdf" and I learned this.

"For Windows Explorer, you can enable PDF thumbnail previews by going to the Preferences in Acrobat or Acrobat Reader and checking the box for "Enable PDF thumbnail preview in Windows Explorer"."

I thought it can't be that easy, can it? So into Adobe I went. Menu>Preferences>General>Basic Tools. Checked the box that said "Enable PDF thumbnail previews in Windows Explorer". Thumbnails show in File Explorer now. It's been 5 days and it's still working.

guys use this method also for domain users and if you using files over netword drives

just add the path of Ip address of the netwrok drive where it says the website as described below and it will work

ust add the path where your files are saved.

1. Go to Internet Options.
2. Go to Security Tab.
3. Go to Trusted sites and click sites.
4. Add the path where your files are saved. Make sure you uncheck the "Require server verification (https:) for all sites in this zone.
5. All done, go ahead and try if it works.

Thanks Hisham, this worked for me! I had the Sharepoint already in my trusted sites with no joy, but today when I put in the specific path for where I keep my Xero invoice downloads, and tested a file saved into a subfolder of that, it worked!

Hi,

Did any of you notice a worsening of deployment speed since this issue about preview for pdf files?

I tried both solutions here (uninstall 25H2, and the powershell command). Neither worked.

The weird thing is some pdfs preview, others wont, in the same folder. Some incompetent security BS I guess.

MS + Adobe would have to be the worst combination

CAN FOR THE LOVE OF GOD TO GET A FIX FOR IT "MICOSOFT"? I PRINTED A FILE AS A PDF IN MY OWN COMPUTER AND CAN'T PREVIEW IT!

if there is share folder then open control panel then internet option, security and trusted sites and add your server ip address, then you can view the pdf file in folder (File explorer preview).

but if this is your personal computer then you need to open pdf file and save again on same location in your computer then you can preview in folder or go to file explorer options and open view and make sure option checked

" Show Preview Handlers in Preview Pane"

I ran into this today. For me, mapping or navigating to the hostname of the location worked. For example, in my situation, the user had a shortcut to the IP address share location (note this is just an example and not a real ip) \1.1.1.1\scans%username% changing the IP address to the hostname of the server \ActualHostName\scans%username% fixed the issue. For some reason using the IP address wouldn't allow the preview to work