Webforms preview Tpl page
I find two solution links, please check them:

Sol-1: https://www.drupal.org/node/1430034 (Most relevant solution)

Sol-2: How to theme a webform - D7 (It another solution to theme webform with another tpl name: webform-form.tpl.php. Here is the link which provide tpl code.)

I guess you need to use node--webform.tpl.php and also add preprocessor in template.php.

function themeName_preprocess_page(&amp;$vars, $hook) {
  if (isset($vars['node'])) {
    $vars['theme_hook_suggestions'][] = 'page__'. $vars['node']-&gt;type;
  }
}


And when you create tpl file you can check preview variable to check and theme accordingly.

If this doesn't help try second solution.