Customer Number in Invoice.pdf

Hi there,

I am an WP-Newbie and am building an Online-Shop for our customers, which order by telephone atm.
Customers shouldn’t be able to register themselves, only be added by an admin manually. Since we already have already customer numbers for each customer, we would like to keep them, and not use the ones wordpress is giving them automatically.
In the User->New User screen, I integrated a new “customer number” (“kundennummer” in German) field, with the following plugin:

<?php
/*
Plugin Name: KUNDENNUMMER IN REGISTRATION FIELD
Plugin URI: https://scriptbaker.com/adding-custom-fields-to-wordpress-user-profile-and-add-new-user-page/
Description: Plugin for adding a custom profile field to WordPress and on the registration page
Author: Siehe Kommentare
Version: 0.1
Author URI:
*/

/*-----Adding Additionnal User Informations-----*/
 
function custom_user_profile_fields($user){
    if(is_object($user))
    {
        $company = esc_attr( get_the_author_meta( 'kundennummer', $user->ID ) );
    }
    else
    {
        $company = null;
    }
?>
Kundennummer
 
<input type="text" class="regular-text" name="kundennummer" value="<?php echo $company;?>" id="kundennummer" />
 
<?php
}
add_action( 'show_user_profile', 'custom_user_profile_fields' );
add_action( 'edit_user_profile', 'custom_user_profile_fields' );
add_action( "user_new_form", "custom_user_profile_fields" );
 
function save_custom_user_profile_fields($user_id){
# again do this only if you can
if(!current_user_can('manage_options'))
return false;
 
# save my custom field
update_user_meta($user_id, 'kundennummer', $_POST['kundennummer']);
}
add_action('user_register', 'save_custom_user_profile_fields');
?>

Now I would like to see that customer number on my pdf invoice. My German market plugin has the following code for the content of the invoice:

<?php
/**
 * Invoice Content
 *
 * @author 		Vendidero
 * @package 	WooCommerceGermanizedPro/Templates
 * @version     1.0
 */

if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly

$newY = $pdf->getY();

?>

<?php if ( $invoice->get_option( 'address_margin_top' ) ) : ?>
	<?php $pdf->setTmpY( $pdf->getY() + $invoice->get_option( 'address_margin_top' ) ); ?>
<?php endif; ?>

<?php if ( $invoice->get_option( 'show_sender_address' ) == 'yes' ) : ?>
	<?php $pdf->writeCustomHTML( implode( ' - ', $invoice->get_sender_address() ), array( 'classes' => array( 'address-header' ) ) ); ?>
<?php endif; ?>

<?php if ( $invoice->get_address() ) : ?>
	<?php $pdf->writeCustomHTML( wpautop( $invoice->get_address() ), array( 'classes' => array( 'address' ) ) ); ?>
<?php endif; ?>

<?php 
	
	$newY = $pdf->getY();
	$pdf->resetTmpY(); 

?>

<?php if ( $invoice->get_option( 'show_sender_address_detail' ) == 'yes' ) : ?>
	<?php $pdf->writeCustomHTML( $invoice->get_template_content( $invoice->locate_template( 'info-right.php' ), $pdf ), array( 'classes' => array( 'address-header-detail' ), 'align' => 'R' ) ); ?>
<?php endif; ?>

<?php if ( $invoice->get_option( 'date_margin_top' ) ) : ?>
	<?php $pdf->setTmpY( $pdf->getY() + $invoice->get_option( 'date_margin_top' ) ); ?>
<?php endif; ?>

<?php $pdf->writeCustomHTML( wpautop( $invoice->get_date( $invoice->get_option( 'date_format' ) ) ), array( 'classes' => array( 'date' ), 'align' => 'R' ) ); ?>

<?php 

	$pdf->resetTmpY(); 

	if ( $newY > $pdf->getY() )
		$pdf->setXY( $pdf->getX(), $newY ); 

?>

<?php if ( $invoice->get_option( 'title_margin_top' ) ) : ?>
	<?php $pdf->setY( $pdf->getY() + $invoice->get_option( 'title_margin_top' ) ); ?>
<?php endif; ?>

<?php $pdf->writeCustomHTML( wpautop( $invoice->get_title_pdf() ), array( 'classes' => array( 'number' ) ) ); ?>

<?php if ( $invoice->get_option( 'table_margin_top' ) ) : ?>
	<?php $pdf->setY( $pdf->getY() + $invoice->get_option( 'table_margin_top' ) ); ?>
<?php endif; ?>

<?php $pdf->writeCustomHTML( $invoice->get_template_content( $invoice->locate_template( 'table.php' ), $pdf ), array( 'classes' => array( 'table' ) ) ); ?>

I think I need a line, that prints me: “Customer Number: XXXX” before the invoice-table.
Does anyone have an idea? Help please…

Best,
Ilke