Write-ProductKeyList.ps1

. .\Get-ProductKey.ps1
$InputCSV = import-csv .\Input.csv -Header Name
$OutputCSV = @()  
$Keys =@()

foreach ($PC in $InputCSV)  
{   
    $objResult = Get-ProductKey -Computername $PC.name        
        
    $checkResult = $Keys -contains $objResult.ProductKey      
    $Keys += $objResult.ProductKey     
    
    $objResult | Add-Member -type NoteProperty -name Duplicate -value $checkResult
    
    $OutputCSV = $OutputCSV + $objResult
    
}  

$OutputCSV | Select-object Computername,OSDescription,ProductKey,Duplicate | export-csv -path .\Output.csv -noType -encoding UTF8