Magento – How to get pdf invoice programmatically

You can customize the invoice layout by modifying this file : Mage_Sales_Model_Order_Pdf_Invoice(app/code/core/Mage/Sales/Model/Order/Pdf/Invoice.php). Of course you need to rewrite the file properly.

Also take a look at these articles for additional info and examples:

1. http://www.atwix.com/magento/customize-magento-pdf-invoice-and-packingslip/
2. http://www.satollo.net/magento-how-to-sligtly-modify-the-invoice-pdf
3. http://www.magentocommerce.com/knowledge-base/entry/custom-pdf-templates/
4. http://www.magentocommerce.com/wiki/5_-_modules_and_development/orders/editing_an_invoice_pdf

We implemented a barcode on the PDF in FireGento_Pdf. In this case, the barcode represents the order number. But you could have a look at the code to see how it is done here. The main part is this:

$barcodeConfig = array(
    'drawText' => false,
    'orientation' => 90,
    'text' => $order->getIncrementId()
);
$rendererConfig = array(
    'verticalPosition' => 'middle',
    'moduleSize' => 0.9
);
// create dummy Zend_Pdf object, which just stores the current page, so that we can pass it in
// Zend_Barcode_Renderer_Pdf->setResource()
$pdf = new Zend_Pdf();
$pdf->pages[] = $page;
/** @var $renderer Zend_Barcode_Renderer_Pdf */
$renderer = Zend_Barcode::factory('code128', 'pdf', $barcodeConfig, $rendererConfig)->setResource($pdf, 0);
// calculate left offset so that barcode is printed on the right with a little margin
$leftOffset = $page->getWidth() - $renderer->getBarcode()->getWidth(true) * $renderer->getModuleSize() - 10;
$renderer->setLeftOffset($leftOffset);
$renderer->draw();