Password protecting a file

[ghost]

is it possible to password protect the actual file?, i have the following code which protects content but need to password protect the actual file.

$phpWord = \PhpOffice\PhpWord\IOFactory::load("$infile");

$documentProtection = $phpWord->getSettings()->getDocumentProtection();
$documentProtection->setEditing('readOnly');
$documentProtection->setPassword("$encryption_key");

$objWriter = \PhpOffice\PhpWord\IOFactory::createWriter($phpWord, 'Word2007');
$objWriter->save("$infile");

Thanks