if($_POST['downloadfile']) {
    $downloadfile = $_POST['downloadfile'];
    header("Cache-Control: public");
    header("Content-Description: File Transfer");
    header("Content-Disposition: attachment; filename= $downloadfile");
    header("Content-Transfer-Encoding: binary");

    @readfile($downloadfile);
    exit;
}

header("Content-Disposition: attachment; filename= basename($downloadfile"));