ACF in another plugin

Can I add a field to another plugin? The field appears in the Administration of the post, but must be printed in this part of the plugin:

// Closing post excerpt container.
$postExcerptHTML .= ‘</div><div class=”subhome”>’ . the_field(‘sub_title’) . ‘</div><div class=”srp_fb”><div id=”fb-root”></div><script src=”https://connect.facebook.net/en_US/all.js#appId=MYID&xfbml=1″></script><fb:like href=”‘ . get_permalink($post->ID) . ‘” send=”false” layout=”button_count” width=”550″ show_faces=”false” font=””></fb:like></div>’;

But doesn’t work!