Kiểm tra tại đây 
4. Next step is to create a hook_theme() function to theame these forms.
function custom_salesforce_theme() {
  return array(
 // this template is containing theme style for update form
    'custom_salesforce_update_form' => array(
      'template' => 'theme/custom_salesforce_update_form',
      'render element' => 'form',
    ),
 // this template is containing theme style for login form
    'custom_salesforce_login_form' => array(
      'template' => 'theme/custom_salesforce_login_form',
      'render element' => 'form',
    ),
 // this template is containing theme style for both forms
    'custom_salesforce_login_and_update' => array(
      'template' => 'theme/custom_salesforce_login_and_update',
      'arguments' => array('combine_form' => NULL),
    ),
  );
}
Note- Don't forget to create three template files inside theme folder inside your module.
5. Next step to write template preprocessor functions to display individual fields in separate template files.
/**
 * Implements Template Preprocessor For User Login().
 */
function template_preprocess_custom_salesforce_login_form(&$variables) {
  $variables['rtc_registered_email'] = drupal_render($variables['form']['rtc_registered_email']);
  $variables['rtc_password'] = drupal_render($variables['form']['rtc_password']);
  $variables['rtc_submit_form'] = drupal_render_children($variables['form']);
}
Mã trên mô tả cách bạn có thể thêm hai biểu mẫu.
Dưới đây  
là cách bạn thêm nó vào tập tin tpl
<?php
$form = drupal_get_form('user_register_form');
print drupal_render($form);
?>
Hy vọng nó giúp :)