How to intetrupt a form submission in drupal
Try adding the validate function as you have added the submit function:

function add_new_article_form_alter(&amp;$form, &amp;$form_state, $form_id){
  if($form_id=='announcement_node_form')
  {
    $form['#after_build'][] = 'add_new_article_after_build';
    $form['account_password'] = array(
        '#title' =&gt; 'Parola',
        '#type' =&gt; 'password',
        '#required' =&gt; TRUE,
    );

    $form["#validate"][] = 'add_new_article_form_validate';
    $form['#submit'][] = 'add_new_article_form_submit';

    return $form;
  }
}