Certainly annoying. I'm going to uninstall this update. I hope they fix this mistake; it's time-consuming.

if you see this update in your windows

2025-10 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5066835)

try this one if none of the above works done this twice and confirm this update mess with preview pane especially pdf or doc files now my preview pane is fine and i set pause update to 5 weeks keeping this update uninstalled in my pc

I had to make a temporary solution and it worked because I'm stuck in Windows 11 Insider Preview and the updates are integrated so you can't uninstall anything - I'll have to reinstall the entire computer after I get the spare computer.
https://www.howtogeek.com/this-is-the-ultimate-file-explorer-replacement-for-windows-11/

win+r - "inetcpl.cpl"- security - trusted sites - sites

Hi. I made a powerscript file to fix this. It will unblock any PDF's on your Desktop, Documents, or Downloads folders or you can do C: and D: drives. Plus it will unlock future PDF's that you download. Just copy past this into a file, say, fix-pdf-preview.ps1, save it. Then open a administrator PowerShell. navigate to where you saved it and then run .\fix-pdf-preview.ps1. It will give you various options. You are welcome!

=========================================================

Fix Windows 11 PDF Preview Issue (KB5066835)

=========================================================

This script fixes the "file you are attempting to preview

could harm your computer" error in Windows File Explorer

Caused by: October 2025 Windows Update KB5066835

=========================================================

Write-Host "=====================================================" -ForegroundColor Cyan

Write-Host " Windows 11 PDF Preview Fix Script" -ForegroundColor Cyan

Write-Host "=====================================================" -ForegroundColor Cyan

Write-Host ""

Check if running as Administrator

$isAdmin = ([Security.Principal.WindowsPrincipal] [Security.Principal.WindowsIdentity]::GetCurrent()).IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator)

if (-not $isAdmin) {

Write-Host "ERROR: This script must be run as Administrator!" -ForegroundColor Red

Write-Host "Right-click on PowerShell and select 'Run as Administrator'" -ForegroundColor Yellow

Write-Host ""

Read-Host "Press Enter to exit"

exit

}

Write-Host "Running as Administrator - OK" -ForegroundColor Green

Write-Host ""

=========================================================

STEP 1: Prevent future files from being blocked

=========================================================

Write-Host "[STEP 1] Configuring registry to prevent future file blocking..." -ForegroundColor Yellow

try {

# Create the registry key if it doesn't exist

$regPath = "HKCU:\Software\Microsoft\Windows\CurrentVersion\Policies\Attachments"



if (-not (Test-Path $regPath)) {

    New-Item -Path $regPath -Force | Out-Null

    Write-Host "  - Created registry key" -ForegroundColor Green

}



# Set the SaveZoneInformation value

New-ItemProperty -Path $regPath -Name "SaveZoneInformation" -PropertyType DWord -Value 1 -Force | Out-Null

Write-Host "  - Set SaveZoneInformation = 1" -ForegroundColor Green

Write-Host "  - Future downloads will no longer be blocked!" -ForegroundColor Green

} catch {

Write-Host "  - ERROR: Failed to modify registry" -ForegroundColor Red

Write-Host "  - $($_.Exception.Message)" -ForegroundColor Red

}

Write-Host ""

=========================================================

STEP 2: Unblock existing files

=========================================================

Write-Host "[STEP 2] Choose which files to unblock:" -ForegroundColor Yellow

Write-Host ""

Write-Host " 1. Downloads folder only (Quick - Recommended)" -ForegroundColor White

Write-Host " 2. Documents folder only" -ForegroundColor White

Write-Host " 3. Desktop folder only" -ForegroundColor White

Write-Host " 4. All three folders (Downloads, Documents, Desktop)" -ForegroundColor White

Write-Host " 5. Entire C: drive (Slow - may take several minutes)" -ForegroundColor White

Write-Host " 6. Entire D: drive (Slow - may take several minutes)" -ForegroundColor White

Write-Host " 7. Both C: and D: drives (Very slow - may take 10+ minutes)" -ForegroundColor White

Write-Host " 8. Custom folder path" -ForegroundColor White

Write-Host " 9. Skip this step" -ForegroundColor White

Write-Host ""

$choice = Read-Host "Enter your choice (1-9)"

$foldersToUnblock = @()

switch ($choice) {

"1" { 

    $foldersToUnblock += "$env:USERPROFILE\Downloads"

}

"2" { 

    $foldersToUnblock += "$env:USERPROFILE\Documents"

}

"3" { 

    $foldersToUnblock += "$env:USERPROFILE\Desktop"

}

"4" { 

    $foldersToUnblock += "$env:USERPROFILE\Downloads"

    $foldersToUnblock += "$env:USERPROFILE\Documents"

    $foldersToUnblock += "$env:USERPROFILE\Desktop"

}

"5" { 

    $foldersToUnblock += "C:\"

}

"6" {

    if (Test-Path "D:\") {

        $foldersToUnblock += "D:\"

    } else {

        Write-Host "  - ERROR: D: drive not found" -ForegroundColor Red

    }

}

"7" {

    $foldersToUnblock += "C:\"

    if (Test-Path "D:\") {

        $foldersToUnblock += "D:\"

    } else {

        Write-Host "  - WARNING: D: drive not found, will only scan C:" -ForegroundColor Yellow

    }

}

"8" {

    $customPath = Read-Host "Enter the full path to the folder (e.g., D:\MyFolder)"

    if (Test-Path $customPath) {

        $foldersToUnblock += $customPath

    } else {

        Write-Host "  - ERROR: Path not found: $customPath" -ForegroundColor Red

    }

}

"9" {

    Write-Host "  - Skipping file unblocking" -ForegroundColor Yellow

}

default {

    Write-Host "  - Invalid choice. Skipping file unblocking." -ForegroundColor Red

}

}

Write-Host ""

foreach ($folder in $foldersToUnblock) {

Write-Host "  - Unblocking files in: $folder" -ForegroundColor Cyan



try {

    $files = Get-ChildItem -Path $folder -Recurse -ErrorAction SilentlyContinue

    $totalFiles = $files.Count

    $unblocked = 0

    

    Write-Host "    Found $totalFiles files to check..." -ForegroundColor White

    

    foreach ($file in $files) {

        try {

            Unblock-File -Path $file.FullName -ErrorAction SilentlyContinue

            $unblocked++

        } catch {

            # Silently continue on errors (files in use, permission issues, etc.)

        }

    }

    

    Write-Host "    Processed $unblocked files successfully!" -ForegroundColor Green

} catch {

    Write-Host "    ERROR: $($_.Exception.Message)" -ForegroundColor Red

}

}

=========================================================

STEP 3: Restart File Explorer

=========================================================

Write-Host ""

Write-Host "[STEP 3] Restart Windows Explorer to apply changes?" -ForegroundColor Yellow

$restart = Read-Host "Restart Explorer now? (Y/N)"

if ($restart -eq "Y" -or $restart -eq "y") {

Write-Host "  - Restarting Windows Explorer..." -ForegroundColor Cyan

Stop-Process -Name explorer -Force

Start-Sleep -Seconds 2

Start-Process explorer

Write-Host "  - Windows Explorer restarted!" -ForegroundColor Green

} else {

Write-Host "  - Skipped. Please restart Explorer manually or reboot your PC." -ForegroundColor Yellow

}

=========================================================

COMPLETION

=========================================================

Write-Host ""

Write-Host "=====================================================" -ForegroundColor Cyan

Write-Host " Script completed!" -ForegroundColor Green

Write-Host "=====================================================" -ForegroundColor Cyan

Write-Host ""

Write-Host "What was done:" -ForegroundColor White

Write-Host " ✓ Registry updated to prevent future file blocking" -ForegroundColor Green

Write-Host " ✓ Existing files unblocked (if selected)" -ForegroundColor Green

Write-Host ""

Write-Host "If you still see the preview warning:" -ForegroundColor Yellow

Write-Host " 1. Restart your computer" -ForegroundColor White

Write-Host " 2. Or consider uninstalling update KB5066835:" -ForegroundColor White

Write-Host " Settings > Windows Update > Update History > Uninstall Updates" -ForegroundColor White

Write-Host ""

Read-Host "Press Enter to exit"