Making File Field description required
If you like you can add to the hook_field_widget_form_alter and then add a validation callback:

  $form['#validate'][] = 'my_validate_function';


Then create a my_validate_function($form, &amp;$form_state) which contains a check on the values and calls a form_set_error($name, $message) if a value is wrong or missing.

/**
 * Implements hook_field_widget_form_alter().
 */
function MYMODULE_field_widget_form_alter(&amp;$element, &amp;$form_state, $context) {
  if ($context['field']['field_name'] == 'field_MYFIELD' &amp;&amp; $context['instance']['widget']['type'] == 'file_generic') {
    $context['form']['#validate'][] = 'my_validate_function';
  }
}

/**
 * Require description to be set.
 */
function my_validate_function($form, &amp;$form_state) {
  if ($form_state['values']['description'] == '') {
    form_set_error('description', 'Description must not be empty.');
  }
}


This may need to be changed above:

$form_state['values']['description']