拡張子にhtmlを付ける

<?php
    add_action( 'init', 'wp_init' );
    if ( ! function_exists( 'wp_init' ) ) {
      function wp_init() {
        global $wp_rewrite;
        $wp_rewrite->use_trailing_slashes = false;
        $wp_rewrite->page_structure = $wp_rewrite->root . '%pagename%.html';
      }
    }
?>