how to use header for download file??

if($status == 'download'){
  $id =$_GET['idfile'];
	
  $query = $modx->db->query("SELECT * FROM uploadf WHERE id = '$id'");
  $data = mysql_fetch_array($query);
 
  $namefile= str_replace(" ","_",$data['name']);

  header("Content-Disposition: attachment; filename=".$namefile);
   
  header("Content-length: ".$data['size']);
  
  header("Content-type: ".$data['type']);
 
  
  $fp  = fopen("assets/docs/".$data['name'], 'r');
  $content = fread($fp, filesize('assets/docs/'.$data['name']));
  fclose($fp);
   
   
   
  return $content;
   
}