Scandir show all pdf files in a folder

$pdffiles = array();
$valid_files = array('pdf');
if(is_dir($clientnumber)){
foreach(scandir($clientnumber) as $file){
$ext = pathinfo($file, PATHINFO_EXTENSION);
if(in_array($ext, $valid_files)){
array_push($pdffiles, $file);
}
}
}
echo json_encode($pdffiles);