PhpOffice\PhpPresentation\PhpPresentation::markAsFinal PHP Method

    public function markAsFinal($state = true)
    {
        return $this->getPresentationProperties()->markAsFinal($state);
    }

 /**
  * Read Custom Properties
  * @param string $sPart
  */
 protected function loadCustomProperties($sPart)
 {
     $xmlReader = new XMLReader();
     $sPart = str_replace(' xmlns="http://schemas.openxmlformats.org/officeDocument/2006/custom-properties"', '', $sPart);
     if ($xmlReader->getDomFromString($sPart)) {
         $pathMarkAsFinal = '/Properties/property[@pid="2"][@fmtid="{D5CDD505-2E9C-101B-9397-08002B2CF9AE}"][@name="_MarkAsFinal"]/vt:bool';
         if (is_object($oElement = $xmlReader->getElement($pathMarkAsFinal))) {
             if ($oElement->nodeValue == 'true') {
                 $this->oPhpPresentation->markAsFinal(true);
             }
         }
     }
 }