Prestashop: duplicate Invoice PDF with new tpl - prestashop

Question

How can I duplicate the Generate Invoice PDF Process in Prestashop? I want to use a different tpl file, but the rest should stay the same.
Let me explain, what I already did:
HTMLTemplateInvoice as HTMLTemplateMahnung and changed Class Name.
Added: const TEMPLATE_MAHNUNG = 'Mahnung'; to the file classes/pdf/PDF.php
Created file mahnung.tpl in root/pdf folder
Added to AdminPdfController.php:
public function processGenerateMahnungPdf() {
if (Tools::isSubmit('id_order')) {
$this->generateMahnungPDFByIdOrder(Tools::getValue('id_order'));
} elseif (Tools::isSubmit('id_order_invoice')) {
$this->generateInvoicePDFByIdOrderInvoice(Tools::getValue('id_order_invoice'));
} else {
die(Tools::displayError('The order ID -- or the invoice order ID -- is missing.'));
}}
AND
public function generateMahnungPDFByIdOrder($id_order)
{
$order = new Order((int)$id_order);
if (!Validate::isLoadedObject($order)) {
die(Tools::displayError('The order cannot be found within your database.'));
}
$order_invoice_list = $order->getInvoicesCollection();
Hook::exec('actionPDFInvoiceRender', array('order_invoice_list' => $order_invoice_list));
$this->generatePDF($order_invoice_list, PDF::TEMPLATE_MAHNUNG);
}
But it's not working. It just doesn't generate the PDF.
Any help?
UPDATE
I had to include the class: require_once _PS_ROOT_DIR_ . '/classes/pdf/HTMLTemplateMahnung.php';
Now its working. Anybody knows why I had to this? I don't see any includes of Core Files :S

Answer 1

Pretashop uses the file cache/class_index.php to keep track of the classes it needs.
Everytime you add a new override, or even a class or controller, you need to delete (or rename) this file. If it doesn't find it, Prestashop will recreate indexing all files in set folders (classes, controllers, overrides, and others).