(PHP 4 >= 4.3.0, PHP 5, PHP 7)
fdf_get_attachment — Extracts uploaded file embedded in the FDF
$fdf_document
   , string $fieldname
   , string $savepath
   )
   Extracts a file uploaded by means of the "file selection" field
   fieldname and stores it under
   savepath. 
  
fdf_documentThe FDF document handle, returned by fdf_create(), fdf_open() or fdf_open_string().
fieldname
savepathMay be the name of a plain file or an existing directory in which the file is to be created under its original name. Any existing file under the same name will be overwritten.
Note:
There seems to be no other way to find out the original filename but to store the file using a directory as
savepathand check for the basename it was stored under.
The returned array contains the following fields:
path - path were the file got stored
    size - size of the stored file in bytes
    type - mimetype if given in the FDF
    
Example #1 Storing an uploaded file
<?php
  $fdf = fdf_open_string($HTTP_FDF_DATA);
  $data = fdf_get_attachment($fdf, "filename", "/tmpdir");
  echo "The uploaded file is stored in $data[path]";
?>