php下載word檔案變亂碼

header("Content-Type: application/octet-stream"); 
header("Expires: 0");
header("Content-Transfer-Encoding: binary");
header("Cache-Control:  must-revalidate, post-check=0, pre-check=0");
header("Content-disposition: attachment; filename=\"$id.doc\"");
$this->load->helper('download');
$file = $this->sub["ulapurl"].$id.".doc";<-檔案位置
$data = file_get_contents($file);
$data=iconv("UTF-8","Big5",$data);<-重點
echo $data;