I'm copying this from the compojoomComment 4.1 documentation:
Docman – com_docman
For the readmore button open the file components/com_docman/themes/yourtheme/templates/
documents/list_item.tpl.php
And place the following code at the end of it:
<!-- START compojoomComment INSERT -->
<div style="clear:both">
<?php
require(JPATH_SITE."/administrator/components/com_comment/plugin/com_docman/josc_com_docma
n_item.php");
?>
</div>
<!-- END OF CompojoomComment INSERT -->
To show the actual comment form in single view of the documents open the file
components/com_docman/themes/yourtheme/templates/documents/document.tpl.php and place the
following code at the end of it:
<!-- START compojoomComment INSERT -->
<div style="clear:both" >
<?php
require_once(JPATH_SITE."/administrator/components/com_comment/plugin/com_docman/josc_com_d
ocman_doc.php");
?>
</div>
<div class="clr"></div>
<!-- END OF compojoomComment INSERT -->
Now go to your Joomla backend components->CompojoomComment->settings click on new and from
the component dropdown list select com_docman and click save. Now you should be able to see
CompojoomComment under docman documents in frontend.
Are you sure that you did everything as described above?
Also change this $option to com_docman.