Exclude pages from WordPress search

functions.php

<?php
/**
 * Exclude footer pages from search
 *
 * @param $query
 *
 * @return array
 */
function your_theme_exclude_pages_from_search( $query ) {
	if ( $query->is_search ) {
		$footer_page = get_page_by_title( 'Footer' );

		$page_ids = array( $footer_page->ID );
		if ( ! is_null( $footer_page ) ) {
			$page = new WP_Query( array(
				'post_parent' => $footer_page->ID,
				'post_type'   => 'page',
			) );

			if ( $page->have_posts() ) {
				while ( $page->have_posts() ) {
					$page->the_post();
					$page_ids[] = get_the_ID();
				}
			}

			$query->set( 'post__not_in', $page_ids );
		}
	}

	return $query;
}

add_filter( 'pre_get_posts', 'your_theme_exclude_pages_from_search' );