Product Categories in invoice.php file

<?php if (!empty($item -> product -> categories)) : ?>
    <?php $c = 1; ?>
    <?php foreach ($item -> product -> categories as $category_id) : ?>
        <?php $wpcoDb -> model = $Category -> model; ?>
        <?php if ($category = $wpcoDb -> find(array('id' => $category_id))) : ?>
            <a href="<?php echo get_permalink($category -> post_id); ?>" title="<?php echo $category -> title; ?>"><?php echo $category -> title; ?></a>
            <?php echo ($c < count($item -> product -> categories)) ? ', ' : ''; ?>
        <?php endif; ?>
        <?php $c++; ?>
    <?php endforeach; ?>
<?php endif; ?>