add_filter( 'pre_get_posts', 'tgm_io_cpt_search' );
/**
* This function modifies the main WordPress query to include an array of
* post types instead of the default 'post' post type.
*
* @param object $query The original query.
* @return object $query The amended query.
*/
function tgm_io_cpt_search( $query ) {
if ( $query->is_search ) {
$query->set( 'post_type', array( 'post', 'doc' ) );
}
return $query;
}