You can do something like that (in the file invoice of the view order via the menu Display->Views):
Code:
$fieldsClass = hikashop_get('class.field');
$fields = $fieldsClass->getFields('backend',$this->order,'order');
if(!empty($fields)){
foreach($fields as $fieldName => $oneExtraField) {
?>
<tr>
<td class="key">
<?php echo $this->fieldsClass->getFieldName($oneExtraField);?>
</td>
<td>
<?php echo $this->fieldsClass->show($oneExtraField,@$this->order->$fieldName); ?>
</td>
</tr>
<?php
}?>
<?php
}
