CComment docs

PhocaDownload – com_phocadownload (Pro feature)

Go to your Joomla backend -> components -> CComment -> settings -> new, from the component dropdown field select com_phocadownload and click next. Save the new configuration. Now you need to make few changes to the phoca view files:

-in /components/com_phocadownload/views/category/tmpl/default.php

after :

<?php defined('_JEXEC') or die('Restricted access');

Add:

JLoader::discover('ccommentHelper', JPATH_ROOT . '/components/com_comment/helpers');

Now navigate to the default_files.php (in the same folder):

Find the following code (around line 408):

echo $pdFileDescBottom;

And after it add:

echo '<div class="pd-buttons">';
echo ccommentHelperUtils::commentInit('com_phocadownload',$v);
echo '</div>';

Now when you navigate to a category in phocadownload you should see a write comment button. (you can style this button with CSS)

To show the comment form when the user goes to single view navigate to components/com_phocadownload/views/file/tmpl/default.php and fine the following code:

if ($this->tmpl['display_file_comments'] == 1) {
    if (JComponentHelper::isEnabled('com_jcomments', true)) {
        include_once(JPATH_BASE.DS.'components'.DS.'com_jcomments'.DS.'jcomments.php');
        $o .= JComments::showComments($v->id, 'com_phocadownload_files', JText::_('COM_PHOCADOWNLOAD_FILE') .' '. $v-
>title);
    }
}

Right after it add:

JLoader::discover('ccommentHelper', JPATH_ROOT . '/components/com_comment/helpers');
echo ccommentHelperUtils::commentInit('com_phocadownload', $v);