(PHP 4, PHP 5 < 5.3.0, PECL fdf SVN)
fdf_set_ap — Set the appearance of a field
$fdf_document,$field_name,$face,$filename,$page_number
   Sets the appearance of a field (i.e. the value of the 
   /AP key).
  
fdf_documentThe FDF document handle, returned by fdf_create(), fdf_open() or fdf_open_string().
field_name
face
       The possible values FDFNormalAP,
       FDFRolloverAP and
       FDFDownAP.
      
filename
page_number
   Returns true on success or false on failure.