title: Add Custom Product Field in WooCommerce 'Order Completed' Emails
body: <p>Is there any way I can add content from a custom product field to 'order completed' WooCommerce emails?</p>
  
  <p>I have added this code to my functions.php in order to save my custom field to the product meta information.</p>
  
  <pre><code>//1.1 Display Activation Instructions field in admin
  add_action('woocommerce_product_options_inventory_product_data', 'woocommerce_product_act_fields');
  function woocommerce_product_act_fields(){
      global $woocommerce, $post;
      echo '&lt;div class="product_custom_field"&gt;';
      woocommerce_wp_text_input(
          array(
              'id' =&gt; '_act',
              'label' =&gt; __('Activation Instructions', 'woocommerce'),
              'desc_tip' =&gt; 'true',
              'description' =&gt; 'Enter the Activation Instructions Link.'
          )
      );    
      echo '&lt;/div&gt;';
  }
  
  //1.2 Save Activation Instructions field in product meta
  add_action('woocommerce_process_product_meta', 'woocommerce_product_act_field_save');
  function woocommerce_product_act_field_save($post_id){
      $woocommerce_act_product_text_field = $_POST['_act'];
      if (!empty($woocommerce_act_product_text_field))
          update_post_meta($post_id, '_act', esc_attr($woocommerce_act_product_text_field));
  }
  </code></pre>
  
  <p>I have also added this code to display a custom text on my 'order completed' woocomerce emails.</p>
  
  <pre><code>add_action( 'woocommerce_email_customer_details', 'bbloomer_add_content_specific_email', 20, 4 );
  function bbloomer_add_content_specific_email( $order, $sent_to_admin, $plain_text, $email ) {
     if ( $email-&gt;id == 'customer_completed_order' ) {
        echo '&lt;h2&gt;Activation &amp; Download Instructions&lt;/h2&gt;&lt;p style="margin-bottom:35px;"&gt;Please refer to 
        our &lt;a href="https://example.com/activation-guides/"&gt;Activation Guides&lt;/a&gt; for detailed 
        activation and download instructions.&lt;/p&gt;';
     }
  }
  </code></pre>
  
  <p>The above code works well and it displays the custom text for all 'order completed' emails. </p>
  
  <p>But, I want to replace the URL part of the text with the custom product field data. The data is different for every product.</p>
  
  <p>Thanks.</p>