Sending data from an iframe with an interactive pdf to a php - php

Question

I have an that displays an interactive pdf form. How do I create a button to get data from the pdf document. Need help please, been on this the whole day.
Here's the php file that supposed to get the pdf data
if(isset($_POST) && is_array($_POST) && count($_POST)){
$data=array();
$data['topmostSubform[0].Page1[0].Applicant_Surname[0]']=$_POST['topmostSubform_0__Page1_0__Applicant_Surname_0_'];
$data['topmostSubform[0].Page1[0].Applicant_FirstName[0]']=$_POST['topmostSubform_0__Page1_0__Applicant_FirstName_0_'];
// need the function definition
require_once'createFDF.php';
// some variables to use
// file name will be <the current timestamp>.fdf
$kui = time();
/*$kui = time();*/
$fdf_file=$kui.'.fdf';
// the directory to write the result in
$fdf_dir=dirname(__FILE__).'/results';
// need to know what file the data will go into
$pdf_doc='http://localhost/uniApp/results/fillsheet.pdf';
// generate the file content
$fdf_data=createFDF($pdf_doc,$data);
// this is where you'd do any custom handling of the data
// if you wanted to put it in a database, email the
// FDF data, push ti back to the user with a header() call, etc.
// write the file out
if($fp=fopen($fdf_dir.'/'.$fdf_file,'w')){
fwrite($fp,$fdf_data,strlen($fdf_data));
/* echo $fdf_file,' written successfully.';*/
system("pdftk fillsheet.pdf fill_form results/". $fdf_file. " output results/$kui.pdf flatten");
$_SESSION['message'] = 'Your application has been updated';
$message = 'written successfully.';
echo $kui,' written successfully.';
}else{
die('Unable to create file:'.$fdf_dir.'/'.$fdf_file);
}
fclose($fp);
}
It works well when it using pure php code, but doesn't work when i try it from the <iframe>