Thanks ! This is works:
<?php
$post_object = get_field('project_name');
if( $post_object ): ?>
<div>
<h4><?php echo get_the_title($post_object->ID); ?></h4>
<span>Post Object Custom Field: <?php the_field('project_description', $post_object->ID); ?></span>
</div>
<?php wp_reset_postdata(); // IMPORTANT - reset the $post object so the rest of the page works correctly ?>
<?php endif; ?>
