Quick Simple example of add_filter – sticking something in the bottom of the_content().
// filter to add stuff to the end of content in posts function add_stuff_to_content($content) { global $post; if ( 'post' != get_post_type() ) { // limit this to only the post type you want to alter return $content; //exit; } $original = $content; $morestuff .= '<div class="stuff">Extra Stuff!!</div>'; $thecontent = $original.$morestuff; // puts more stuff right after post return $thecontent; } add_filter(the_content, add_stuff_to_content);