Registry.Pol Viewer

RegistryPolViewer.ps1

#Requires -Modules GPRegistryPolicyParser
#Requires -Version 5

Import-Module -Name GPRegistryPolicyParser -WarningAction Ignore
Add-Type -AssemblyName System.Windows.Forms

$Script:response = [System.Windows.Forms.MessageBox]::Show("Do you want to open current hives?`n`nClick Yes to display current hives on this computer.`nClick No to pick a `'registry.pol`' file to read.", "Open current hives?", [System.Windows.MessageBoxButton]::YesNoCancel, [System.Windows.MessageBoxImage]::Question)

switch ($Script:response)
{
    'Yes' { $Script:OpenHive = $true }
    'No' { $Script:OpenHive = $false }
    Default { return }
}

if ($Script:OpenHive)
{
    $Script:AdminSession = ((New-Object Security.Principal.WindowsPrincipal([Security.Principal.WindowsIdentity]::GetCurrent())).IsInRole([Security.Principal.WindowsBuiltInRole]::Administrator))

    if ($Script:AdminSession)
    {
        $Script:Selected = @("CurrentUser", "LocalMachine") | Out-GridView -Title "Choose a hive" -OutputMode Single
    }
    else
    {
        $Script:Selected = @("CurrentUser") | Out-GridView -Title "Choose a hive" -OutputMode Single
    }

    if ($null -eq $Script:Selected)
    {
        Write-Output "No hives selected."
        return
    }
    else
    {
        Write-Output $Script:Selected
    }

    # No need to use 'Entries' parameter as the GridView provides filtering options
    try
    {
        Read-RegistryPolicies -Division $Script:Selected | Out-GridView -Title "Registry.Pol Content [$Script:Selected]" -Wait -Verbose
    }
    catch
    {
        $null = [System.Windows.Forms.MessageBox]::Show($Error[0].Exception.Message, "Warning", [System.Windows.Forms.MessageBoxButton]::OK, [System.Windows.Forms.MessageBoxImage]::Exclamation)
    }
    
}
else
{
    $Script:dialog = [System.Windows.Forms.OpenFileDialog]::new()
    $Script:dialog.CheckFileExists = $true
    $Script:dialog.CheckPathExists = $true
    $Script:dialog.DefaultExt = '.pol'
    $Script:dialog.Filter = 'Registry Policy file (*.pol)|*.pol'
    $Script:dialog.Title = 'Open a registry.pol file'
    $Script:dialog.Multiselect = $false
    $Script:response = $Script:dialog.ShowDialog()

    if($Script:response -eq 'OK')
    {
        try
        {
            Read-PolFile -Path $Script:dialog.FileName | Out-GridView -Title "Registry.Pol Content [$($Script:dialog.FileName)]" -Wait -Verbose
        }
        catch
        {
            $null = [System.Windows.Forms.MessageBox]::Show($Error[0].Exception.Message, "Warning", [System.Windows.MessageBoxButton]::OK, [System.Windows.MessageBoxImage]::Exclamation)
        }
    }
}

The following is required on line 6 if you want to be able to run this directly from PowerShell Console instead of ISE.
Add-Type -AssemblyName PresentationFramework

Read More about it here:
https://inthetechpit.com/2019/12/05/unable-to-find-type-system-windows-messagebox-error-powershell/