wp_content in plugon not placing file correctly…..

I am creating a simple plugin that I want to put some info below a post.

I am using the the_content hook to try and place the code below posts….

Here is my code:

<?php
add_filter('the_content','function_name');
?>

<?php
function function_name($content = '') {
$content .= include('wp-content/plugins/postfootplugin/codeforpostfoot.php');
return $content;
}
?>

It works great except for the fact that it appears at the top of the post under the title and not below the post under the content as I want…. all other plugins I look at seem to use this same hook!

Any ideas?

Thanks ??