title: Opencart module development - Inject javascript/html code in some pages
body: <p>I'm a beginner on Opencart and just started developing a module for Opencart which it must inject some lines of javascript and html code in these pages:
  - Cart Page
  - Product Page
  - Confirmation Order Page
  - Register form page</p>
  
  <p>The official documentation doesn't have informations about how can i do that, I've tried to find a good documentation about OpenCart but I didn't find anything.</p>
  
  <p>I need help. How can I do that?</p>