How to add a line at the end of all pages?

Goodmorning.
I use that code to add a line at the end of all post.

function diww_add_post_content($content) {
	if (is_single()) {
		$content .= '<p><div id="newsletter-box">? ?????????? ???? ???????????? ?????????. ???????? ???????? ????  <a title="???? ??????." href="">????? ??????</a></div></p>';
	}
	return $content;
}
add_filter ('the_content', 'diww_add_post_content', 0);

How can i do that for pages also.
what do i need to change on that code?
Thanks a lot.