Add "Note to Customer" to the PDF invoice, this code needs WooCommerce PDF Invoices & Packing Slips plugin

functions.php

/** Add "Note to Customer" to the PDF invoice, this code needs WooCommerce PDF Invoices & Packing Slips plugin
 *
 * https://www.nuno-sarmento..com
*/

add_action( 'wpo_wcpdf_after_order_details', 'ns_add_note_to_customer_to_PDF_invoice' );
function ns_add_note_to_customer_to_PDF_invoice() {
  global $wpo_wcpdf;
  $wpo_wcpdf->order_notes(); 
}