title: running ubuntu command from PHP code
body: <p>I want to convert a pdf into html in <code>PHP</code> by running this command </p>
  
  <pre><code>pdftohtml -i -c test/invoice.pdf test/invoice.html
  </code></pre>
  
  <p>but it's not working using this <code>PHP</code> code</p>
  
  <pre><code>$data=exec('pdftohtml -i -c test/invoice.pdf test/invoice.html');
  </code></pre>