PHP readfile() of external URL

Can I use external URLs in readfile()?

    header('Content-type: application/pdf');
    header('Content-Transfer-Encoding: binary');
    header('Content-Disposition: inline; filename="'.$file.'" ');
    //header('Content-Length: ' . filesize("http:...z/pub/".$file.'.pdf'));
    @readfile("http://...z/pub/".$file.'.pdf');