Source code for https://victorfont.com/add-cpts-to-wordpress-searches/

confine_the_search.php

<?php

if ( ! is_admin() && $query->is_main_query() && $query->is_search ) {

vmf_filter_search.php

<?php

dd_filter('pre_get_posts', 'vmf_filter_search');
function vmf_filter_search($query) {
	if ( $query->is_search ) {
		$query->set( 'post_type', array('post', 'page', 'portfolio') );
	};
	return $query;
};