$presentation->SaveAs("SAVED_" . $filename);
$presentation->Close;
undef $ppt; # Clean up Powerpoint
$mw->messageBox (-title => "message", -message=>"DONE!", -icon=> 'info');

##</code><code>##

our $ppt;
sub save_PPT {
# ...
$ppt ||= Win32::OLE->GetActiveObject('PowerPoint.Application');
# ... and also later:
$ppt ||= Win32::OLE->new(
            'PowerPoint.Application', sub { $_[0]->Quit }
        ) or return 'error';
# ---