Hi Fred,
You can simply remove these two lines:
<th class="price"><?php _e('Price', 'wpo_wcpdf'); ?></th>
<td class="price"><?php echo $item['order_price']; ?></td>
But it looks like you have a heavily modified template, so I suggest that you contact the person that made those modifications for you – he or she will know exactly what to remove.
What kind of custom fields do you want to translate? Or do you just want to make the labels to the fields translatable? In the latter case, you can either work with string translation, or add them to the wpo_wcpdf textdomain (or your themes textdomain) and create your own translation files.
i.e. instead of:
<?php $wpo_wcpdf->custom_field('custom_fieldname', 'Custom field:'); ?>
you use:
<?php $wpo_wcpdf->custom_field('custom_fieldname', __( 'Custom field:', 'wpo_wcpdf') ); ?>
Note that for the PDF invoice plugin to pick up those translations automatically in the order language, you need the professional extension.
Hope that helps!