There are so many third party libraries or extensions that are available for generating/tracking barcodes.

Today I’m going to share with you that how we can easily add unique barcodes in our pdf using Magento default Zend library.

First, you have to create [Vendor Name]/[Module Name]/etc/di.xml in your existing module or create a new module and add the below code:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="MagentoSalesModelOrderPdfInvoice">
        <plugin name="barcodes_pdf_invoice" type="[Vendor Name][Module Name]PluginInvoice" sortOrder="10" />
    </type>
</config>

Then you have to create a plugin file [Vendor Name][Module Name]PluginInvoice.php and add the below code:

<?php

namespace [Vendor Name][Module Name]Plugin;

use MagentoFrameworkAppConfigScopeConfigInterface;

class Invoice
{
     /**
     * Configuration barcode enable XML path
     */
    const XML_PATH_BARCODES_ENABLED = 'barcodes/general/eb_barcodes_active';
    /**
     * @var ScopeConfigInterface
     */
    private $scopeConfig;
    
    public function __construct(
        ScopeConfigInterface $scopeConfig
    ) {
        $this->scopeConfig = $scopeConfig;
    }
    
    public function beforeInsertDocumentNumber($subject, $page, $text)
    {
        if ($this->scopeConfig->isSetFlag(self::XML_PATH_BARCODES_ENABLED)) { //Here you will check your custom condition like enable/disable
            $docHeader = $subject->getDocHeaderCoordinates();
            $image = $this->generateBarcode($text);
            $page->drawImage($image, $docHeader[2] - 150, $docHeader[1] + 5, $docHeader[2] + 8, $docHeader[1] +50); //You will adjust barcode image place or height/width as per your requirement
        }
    }

    protected function generateBarcode($text)
    {
        $config = new Zend_Config([
            'barcode' => 'code128',
            'barcodeParams' => [
                'text' => $this->extractInvoiceNumber($text),
                'drawText' => true
            ],
            'renderer' => 'image',
            'rendererParams' => ['imageType' => 'png']
        ]);
        $barcodeResource = ZendBarcodeBarcode::factory($config)->draw();
        ob_start();
        imagepng($barcodeResource);
        $barcodeImage = ob_get_clean();
        $image = new Zend_Pdf_Resource_Image_Png('data:image/png;base64,' . base64_encode($barcodeImage));
        return $image;
    }

    protected function extractInvoiceNumber($text)
    {
        $array_of_words = explode("#", $text);
        return $array_of_words[1];
    }
}

After creating both files run php bin/magento cache:flush and see any invoice pdf barcodes are printed as below.