How to set custom tab on product detail page to download and show pdf links?

If you want to set one more custom tab to show pdf & download them then follow the below steps.

Step 1: Create a file like app/code/Magemonkeys/Custompdftab/registration.php

<?php 
MagentoFrameworkComponentComponentRegistrar::register(
    MagentoFrameworkComponentComponentRegistrar::MODULE,
    'Magemonkeys_Custompdftab',
    __DIR__
);
?>

Step 2: Create a file like app/code/Magemonkeys/Custompdftab/etc/module.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Magemonkeys_Custompdftab" setup_version="1.0.0">
        <sequence>
            <module name="Magento_Catalog"/>
        </sequence>
    </module>
</config>

Step 3: Create a file like app/code/Magemonkeys/Custompdftab/Helper/Data.php

<?php

namespace MagemonkeysCustompdftabHelper;

use MagentoFrameworkAppHelperAbstractHelper;
use MagentoFrameworkAppHelperContext;

class Data extends AbstractHelper
{
    public function stringToTable($text, $colSeparator = '|', $rowSeparator = '||')
    {
        $rows = explode($rowSeparator, $text);
        if (!$rows) return false;
        $html = '<table>';
        foreach ($rows as $row) {
            if ($row) {
                $html .= '<tr>';
                $columns = explode($colSeparator, $row);
                $w=count($columns);
                foreach ($columns as $column) {
                    $html .= '<td style="width:'. 100/$w .'%">' . $column . '</td>';
                }
                $html .= '</tr>';
            }
        }
        $html .= '</table>';

        return $html;
    }

    public function applicationsRender($applications,  $separator = "||"){

        //echo 'called';exit;
        if(!$applications)
            return;

        $html = '';
        $_elements = '';

        if(strpos($applications,':') > 0) {
            $_items = explode('.',$applications);
            natcasesort($_items);
            foreach($_items as $_item){
                $_item = explode(':',$_item);

                if($_item[0] == '')
                    continue;

                $html .= '<ul class="applications">';
                $html .= trim($_item[0]).': ';
                $_elements = @explode($separator,$_item[1]);

                foreach ($_elements as $element){
                    $html .= '<li>'.trim($element).'</li>';
                }
                $html .= '</ul>';
            }
        } else {
            $html .= '<ul class="applications">';
            $_items = explode($separator,$applications);
            natcasesort($_items);
            foreach ($_items as $_item){
                $html .= '<li>'.$_item.'</li>';
            }
            $html .= '</ul>';
        }

        return $html;

    }
}

Step 4: Create a file like app/code/Magemonkeys/Custompdftab/view/frontend/layout/catalog_product_view.xml

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <body>
        <referenceBlock name="product.info.details">
            <block class="MagentoCatalogBlockProductView" name="custom-tab" template="Magemonkeys_Custompdftab::product/view/details/custom_tab.phtml" group="detailed_info">
                <arguments>
                    <argument name="css_class" xsi:type="string">newtabclass</argument>
                    <argument translate="true" name="title" xsi:type="string">Documentatie</argument>
                    <argument name="sort_order" xsi:type="string">60</argument>
                </arguments>
            </block>
        </referenceBlock>
    </body>
</page>

Step 5 : Create file like app/code/Magemonkeys/Custompdftab/view/frontend/templates/product/view/details/custom_tab.phtml

<?php 
    $_product = $block->getProduct();
    $sku = $_product->getSku();
    $file = $_product->getAgreementFile();
    $objectManager = MagentoFrameworkAppObjectManager::getInstance();

    $fileSystem = $objectManager->create('MagentoFrameworkFilesystem');
    $mediaPath = $fileSystem->getDirectoryRead(MagentoFrameworkAppFilesystemDirectoryList::MEDIA)->getAbsolutePath();

    $dir = '/'.$mediaPath.'/'.'catalog/product/file/'.$file;
    $dir2 = '/'.$mediaPath.'/'.'file/'.$sku;

    $flag = FALSE;
    $flag1 = true;
?>
<?php if(file_exists($dir) && $file != ''):{
        $flag1 = false;
        if($file){ $flag = TRUE; } ?>
        <a class="download-file" href="<?php echo $block->getBaseUrl(); ?>pub/media/catalog/product/file/<?php echo basename($file) ?>" target="_blank"><?php echo str_replace('.pdf', '', $file) ?></a>
    <?php } elseif(file_exists($dir2) && $flag1):{
      if ($dh = opendir($dir2)){   
        while (($file = readdir($dh)) !== false){
          if ($file != '.' && $file != '..') {
            if($file){ $flag = TRUE;  }?>
            <a class="download-file1" href="<?php echo $block->getBaseUrl(); ?>pub/media/file/<?php echo $sku.'/'.basename($file) ?>" target="_blank"><?php echo str_replace('.pdf', '', $file) ?></a>
    <?php 
            }     
          }
        }
      }
    ?>
<?php else: ?>
    <?php echo "There is no file"; ?>
<?php endif; ?>

<?php if($flag == TRUE): ?>
    <script>
        require(['jquery', 'jquery/ui'], function($){
           $('#tab-label-custom-tab').css('display','block');
        });
    </script>
<?php endif; ?>

That’s it…

Now, you can check your product detail page. Your custom tab will be showing after all default tabs.