How to modify bill to accomplish this?

[PrestashopTrackglobe]

At the store I am creating http://www.eluniversodelperro.com store I added a new button in the "Bills" to generate the invoice or order from suppliers; gusari me know:

1 - I have to change so that instead of calling a function / class / call me PDF2.php PDF.php
2 - I would like to appear the purchase price to the supplier (if I quivoco 'wholesale_price')

the thing is that the file pdf.php see this piece (which if I remember correctly is that I have to change, I've got to show me the reference pro

/**
  * Product table with references, quantities...
  */
  public function ProdReturnTab()
  {
     global $ecotax;

     $header = array(
        array(self::l('Description'), 'L'),
        array(self::l('Reference'), 'L'),
        array(self::l('Qty'), 'C')
     );
     $w = array(110, 25, 20);
     $this->SetFont(self::fontname(), 'B', 8);
     $this->SetFillColor(240, 240, 240);
     for ($i = 0; $i < sizeof($header); $i  )
        $this->Cell($w[$i], 5, $header[$i][0], 'T', 0, $header[$i][1], 1);
     $this->Ln();
     $this->SetFont(self::fontname(), '', 7);

     $products = OrderReturn::getOrdersReturnProducts(self::$orderReturn->id, self::$order);
     foreach ($products AS $product)
     {
        $before = $this->GetY();
        $this->MultiCell($w[0], 5, Tools::iconv('utf-8', self::encoding(), $product['product_name']), 'B');
        $lineSize = $this->GetY() - $before;
        $this->SetXY($this->GetX()   $w[0], $this->GetY() - $lineSize);
        $this->Cell($w[1], $lineSize, ($product['product_reference'] != '' ? Tools::iconv('utf-8', self::encoding(), $product['product_reference']) : '---'), 'B');
        $this->Cell($w[2], $lineSize, $product['product_quantity'], 'B', 0, 'C');
        $this->Ln();
     }
  }
........................

I liked that all I calculate everything as the price of the purchase price from the wholesaler, but do not know what exactly I have to change, finally, I also like that when you generate the PDF, if there are 4 clients shopping, I'll generate the same but priced provider, and I want at the very end, I calculate the sum of all products excluding VAT, of all the taxes, and total.

Anybody can help me a bit to accomplish this?

Thank you very much and best regards