Add .html to Woocommerce permalinks [closed]

This is the simplest way to add .html, which involves overriding the default permastructure:

function wpse_178112_permastruct_html( $post_type, $args ) {
    if ( $post_type === 'product' )
        add_permastruct( $post_type, "{$args->rewrite['slug']}/%$post_type%.html", $args->rewrite );
}

add_action( 'registered_post_type', 'wpse_178112_permastruct_html', 10, 2 );

http://codex.wordpress.org/Function_Reference/add_permastruct

For categories:

function wpse_178112_category_permastruct_html( $taxonomy, $object_type, $args ) {
    if ( $taxonomy === 'product_cat' )
        add_permastruct( $taxonomy, "{$args['rewrite']['slug']}/%$taxonomy%.html", $args['rewrite'] );
}

add_action( 'registered_taxonomy', 'wpse_178112_category_permastruct_html', 10, 3 );