Add Google web font externally in DRUPAL 7

Find the template.php in your custom theme folder edit the template.php and add this function

function mytheme_preprocess_html(&$variables) {
drupal_add_css('http://fonts.googleapis.com/css?family=PT+Sans:400,700,400italic,700italic&subset=latin,cyrillic', array('type' => 'external'));
}

NOTE:
 change the mytheme with your theme name!.

For more Check this Out...
http://blog.morethanthemes.com/post/9951799439/drupal-7-tutorial-adding-google-web-fonts-as-external