<?php

/**
 * Hook structure.
 */
function hook_node_view($node, $view_mode, $langcode) {
  // Do something here.
}

/**
 * Implements hook_node_view
 */
function my_module_name_node_view($node, $view_mode, $langcode) {
  $node->content['my_additional_field'] = array(
    '#markup' => '<p>Some additional content.</p>',
    '#weight' => 10,
  );
}