gistfile1.php

<?php

function restrict_post_content_form_1($content) {
	if( get_post_meta( get_the_ID(), 'protected', true ) == 'yes' && !is_user_logged_in() && !isset( $_COOKIE['form-1-complete'] ) ) {
				return gravity_form(1, false, false, false) . '<p>This article is only available to subscribers to our newsletter. You may subscribe using the form above.</p>';
	}
	else {
		return $content;
	}
}

add_filter( 'the_content', 'restrict_post_content_form_1' );