One of our clients was looking to add the Barcode using OrderIncrement id.

To achieve that I used picqer/php-barcode-generator library in Magento. You can follow the remaining steps only after installing the library.

Step 1: Create a Plugin and define that plugin di.xml. Use the below code and add it to the di.xml file.

<type name="MagentoSalesModelOrderPdfInvoice">
    <plugin name="barcodes_pdf_invoice" type="MagemonkeysBarcodesPluginInvoice" sortOrder="10" />
</type>

Step 2: Create a Invoice.php file under Plugin under this folder “app/code/Magemonkeys/Barcode/Plugin“.

<?php
/**
 * @category Print Barcode On Invoice PDF
 * @package  Magemonkeys_Barcodes
 * @author   Abbacus Team
 */
namespace MagemonkeysBarcodesPlugin;

use MagentoFrameworkAppConfigScopeConfigInterface;
use PicqerBarcodeBarcodeGeneratorPNG;

class Invoice
{
    /**
     * @var ScopeConfigInterface
     */
    private $scopeConfig;
    /**
     * @var MagentoSalesModelOrderInvoice
     */
    private $invoiceModel;
    
    /**
     * 
     * @param ScopeConfigInterface $scopeConfig
     * @param MagentoSalesModelOrderInvoice $invoiceModel
     */
    public function __construct(
        ScopeConfigInterface $scopeConfig,
        MagentoSalesModelOrderInvoice $invoiceModel
    ) {
        $this->scopeConfig = $scopeConfig;
        $this->invoiceModel = $invoiceModel;
    }
    
    /**
     * 
     * @param string $subject
     * @param object $page
     * @param string $text
     */
    public function beforeInsertDocumentNumber($subject, $page, $text)
    {
        $docHeader = $subject->getDocHeaderCoordinates();
        $image = $this->generateBarcode($text);
        $page->drawImage($image, $docHeader[2] - 150, $docHeader[1] + 20, $docHeader[2] , $docHeader[1] +55);
    }
    
    /**
     * 
     * @param string $text
     * @return Zend_Pdf_Resource_Image_Png
     */
    protected function generateBarcode($text)
    {
        $invoiceIncrement = $this->extractInvoiceNumber($text);
        $invoice = $this->invoiceModel->loadByIncrementId(trim($invoiceIncrement));
        $order = $invoice->getOrder();
        $orderIncrementId = $order->getIncrementId();
        $generator = new BarcodeGeneratorPNG;
        $image = new Zend_Pdf_Resource_Image_Png('data:image/png;base64,' . base64_encode($generator->getBarcode($orderIncrementId, $generator::TYPE_CODE_128)));
        return $image;
    }
    
    /**
     * 
     * @param string $text
     * @return string
     */
    protected function extractInvoiceNumber($text)
    {
        $array_of_words = explode("#", $text);
        return $array_of_words[1];
    }
}

Now, when you print the Invoice PDF, the barcode will be shown on the top of the PDF. Happy coding. 🙂