I know this is old but for anyone having the same problem with the formatting after you add the:
<?php echo $post->post_content; ?>
To your PHP page out side of WP…All you have to do is go in to the ADMIN section of WP > go to manage and then to your post > switch it to code view and add your <p></p> tags and what not to what you are looking to format.
I think what the echo code does is simply pull the text that you entered. So, just add the proper HTML formatting tags and it will pull that too.
