title: Use Woocommerce functions in custom php files
body: <p>I am a total beginner in programming with PHP. I wanted to create a PHP file in which the <code>order_status</code> from a predefined order (in my case 108) gets changed to completed. </p>
  
  <p>Therefore I need the woocommerce functions <code>get_order($ID)</code> and <code>update_status</code> but I do not know how to use them in my PHP. I hope you understand my problem. From Java I could imagine that I need to get an instance from a class or something like that? </p>
  
  <p>Here is the code I have so far:</p>
  
  <pre><code>&lt;?php $ord = new WC_Order(108); $ord-&gt;update_status('completed'); ?&gt;
  </code></pre>
  
  <p>When I open the page I receive the following error:</p>
  
  <pre><code>Fatal error: Uncaught Error: Class 'WC_Order' not found (...)
  </code></pre>