How to add an excerpt and read more link to a page?

Not sure if this is what you looking for… To display excerpt of specific page, you can use this code:

<?php
    $post_id = 2; // substitute to your page id
    $my_post = get_post($post_id);
    echo "<p>$my_post->post_excerpt</p>";
    echo '<a href="'.get_permalink( $post_id ).'">read more</a>';
?>