Converting pdf form data to txt through pdftk

Question

I have uploaded pdftk in the webmin server and using following code:

<?php
exec("/usr/bin/pdftk Test.pdf dump_data_fields > form-fields.txt"); 
?>

Unfortunately I am not getting any value in txt file. I cannot realize where I am making mistake.

On the other hand I have tested in local server xampp with following script. In xampp server I am getting value in the txt file.

        //in xampp
<?php
    exec("C:\\LocalServer\\htdocs\\pdf\\usr\\bin\\pdftk Test.pdf dump_data_fields > form-fields.txt"); 
<?

Here is pdftk https://dl.dropboxusercontent.com/u/70850345/usr.zip