Add custom variables to PMPro PDF Invoices Templates

my-own-pmpro-pdf-variable-template.php

<?php
/**
 * This example shows you how to create custom variables for your email templates.
 * All customers that have purchased an 'All Access' pass get up to 5 custom variables created to help get you started.
 * https://yoohooplugins.com/all-access
 */
function my_custom_pmpro_pdf_variable( $data_array, $user, $order_data ) {
	$data_array['{{user_name_example}}'] = $user->user_nicename;
	return $data_array;
}
add_filter( 'pmpro_pdf_invoice_custom_variables', 'my_custom_pmpro_pdf_variable', 10, 3 );