Append html after node content in custom module in Drupal 7
You can use the node view alter hook in your module to add/change your node object:


  This hook is called after the content has been assembled in a structured array and may be used for doing processing which requires that the complete node content structure has been built.


If you have devel enabled, you can dpm($node) inside your node_view_alter function to see the node structure and then you can add to it as needed from the module.