Hi.
1. you need to create PdfDeliverySlipController.php (you can find similar ./controllers/front/PdfInvoiceController.php)
2. create your own hook in the module (for example: displayDeliverySlipUrl and in the parameter you will get id_order)
3. create your own TPL template in the module
4. insert your own hook in history.tpl e.g. {hook h='displayDeliverySlipUrl' id_order=$order.details.id}
result: