WordPres filter content if find any certain word

filter-content.php

<?php
/**
 * Filter content if find any certain word.
 * @author Razon Komar Pal
 */
function ic_filter_content_sample($content)
{
	// for single post
	if (is_single()) {
		$new_content = '<p>This is added to the bottom of all post and page content</p>';
		$search = 'Welcome to WordPress';
		if (strpos($content, $search) !== false) {
			$content = $new_content . $content;
		}
		return $content;
	}
	return $content;
}
add_filter('the_content', 'ic_filter_content_sample');