(PHP 4, PHP 5 < 5.3.0, PECL fdf SVN)
fdf_save — Save a FDF document
$fdf_document
   [, string $filename
  ] ) : boolSaves a FDF document.
fdf_documentThe FDF document handle, returned by fdf_create(), fdf_open() or fdf_open_string().
filenameIf provided, the resulting FDF will be written in this parameter. Otherwise, this function will write the FDF to the default PHP output stream.
   成功时返回 TRUE, 或者在失败时返回 FALSE。