A lot of free theme developers try to force those who use their themes to display a link back to their web site in exchange for providing a free template.
The odd looking code that you posted above is base64 encrypted code that when decrypted simply renders the usual footer HTML tags.
Here’s what it decrypts into…
?>
<div id="footer">
<p>Copyright <?php bloginfo('name'); ?> . <?php if(is_home()) : ?><a href="https://1acnemedication.com/" title="Acne treatment ">Acne treatment </a><?php endif; ?></p>
</div>
</div>
</div>
<?php wp_footer(); ?>
</body>
</html>
<?
If you remove the encrypted code, be sure that you close your HTML tags properly, since the theme’s author hid those tags within the encrypted text. Take note that there is also an opening PHP tag as well.
Hope that helps!