running Pdf2htmlEX on linux using php

Question

Kindly I request your help on the following issue: I am using pdf2htmlEX to convert my pdf files to HTML. The tool is working perfectly in WAMP; however, when I implement it on my Linux server, the tool is not working.

My php code:

<?php $cmd=  "pdf2htmlEX --zoom 1.3 sample.pdf sample.html";
exec($cmd, $output, $return);?>

Note that I have tested exec command and it is enabled. Moreover, the directory is rewritable.

I am running the code from my browser

Your help is highly appreciated.

Thank you, Rasha