Enumerates Windows file extensions that register for a Preview or Thumbnail handler

EnumShellHandlers.ps1

$hkcrPath = "Registry::HKEY_CLASSES_ROOT"
$previewClsid = "{8895b1c6-b41f-4c1c-a562-0d564250836f}"
$thumbnailClsid = "{E357FCCD-A995-4576-B01F-234630154E96}"

Write-Host "--------------------------------------------------"
Write-Host "Enumerating file type extensions that register" -ForegroundColor Cyan
Write-Host "preview or thumbnail handlers..." -ForegroundColor Cyan
Write-Host "--------------------------------------------------"

$extensions = Get-ChildItem -Path $hkcrPath | Where-Object { $_.PSChildName -like ".*" }

foreach ($ext in $extensions) {
    $extName = $ext.PSChildName
    
    # 1. Attempt to get the ProgID from the extension's (default) value
    $progId = (Get-ItemProperty -Path "$hkcrPath\$extName" -Name "(default)" -ErrorAction SilentlyContinue)."(default)"
    
    $previewGuid = $null
    $thumbnailGuid = $null
    $previewSource = $null
    $thumbnailSource = $null

    # 2. Check direct Extension paths first (these usually override ProgIDs)
    $extPreviewPath = "$hkcrPath\$extName\ShellEx\$previewClsid"
    $extThumbnailPath = "$hkcrPath\$extName\ShellEx\$thumbnailClsid"
    
    if (Test-Path -Path $extPreviewPath -ErrorAction SilentlyContinue) {
        $previewGuid = (Get-ItemProperty -Path $extPreviewPath -Name "(default)" -ErrorAction SilentlyContinue)."(default)"
        $previewSource =  "Registered for '$extName' directly"
    }
    
    if (Test-Path -Path $extThumbnailPath -ErrorAction SilentlyContinue) {
        $thumbnailGuid = (Get-ItemProperty -Path $extThumbnailPath -Name "(default)" -ErrorAction SilentlyContinue)."(default)"
        $thumbnailSource = "Registered for '$extName' directly"
    }

    # 3. If missing from Extension, check the ProgID (if one exists)
    if ($progId -and ($progId -is [string]) -and ($progId.Trim() -ne "")) {
        
        $progPreviewPath = "$hkcrPath\$progId\ShellEx\$previewClsid"
        $progThumbnailPath = "$hkcrPath\$progId\ShellEx\$thumbnailClsid"

        if (-not $previewGuid -and (Test-Path -Path $progPreviewPath -ErrorAction SilentlyContinue)) {
            $previewGuid = (Get-ItemProperty -Path $progPreviewPath -Name "(default)" -ErrorAction SilentlyContinue)."(default)"
            $previewSource = "Registered for ProgID '$progId'"
        }

        if (-not $thumbnailGuid -and (Test-Path -Path $progThumbnailPath -ErrorAction SilentlyContinue)) {
            $thumbnailGuid = (Get-ItemProperty -Path $progThumbnailPath -Name "(default)" -ErrorAction SilentlyContinue)."(default)"
            $thumbnailSource = "Registered for ProgID '$progId'"
        }
    }
    
    # 4. Output if either handler was found in either location
    if ($previewGuid -or $thumbnailGuid) {
        [PSCustomObject]@{
            Extension            = $extName
            ProgID               = $progId
            PreviewHandlerGUID   = $previewGuid
            PreviewSource        = $previewSource
            ThumbnailHandlerGUID = $thumbnailGuid
            ThumbnailSource      = $thumbnailSource
        }
    }
}