Add-Type -AssemblyName System.Windows.Forms
$FileBrowser = New-Object System.Windows.Forms.OpenFileDialog -Property @{
    InitialDirectory = [Environment]::GetFolderPath('Desktop')
    Multiselect = $true # Multiple files can be chosen

}

[void]$FileBrowser.ShowDialog()

$path = $FileBrowser.FileNames;

If($FileBrowser.FileNames -like "**") {

    # Do something before work on individual files commences
    $FileBrowser.FileNames #Lists selected files (optional)

    foreach($file in Get-ChildItem $path){
    Get-ChildItem ($file) |
        ForEach-Object {
            Set-ItemProperty -Path $path -Name IsReadOnly -Value $true
            compact /C $_.FullName
        }
    }
    # Do something when work on individual files is complete
}

else {
    Write-Host "Cancelled by user"
}