function mymodule_form_alter(&$form, &$form_state, $form_id) {
 //here's some code like
  // if ($contenttype == 'article') {
  //add more fields

     $form['#tree'] = TRUE;
     $form['#submit'][] = 'mymodule_submit';

//}

}

function mymodule_submit($form, &$form_state) {
  drupal_set_message('The form has been submitted');
  dpm($form_state);
}