You can do this with a small code snippet:
add_action( 'wpo_wcpdf_after_order_details', 'wpo_wcpdf_balance_due_paid', 10, 2 );
function wpo_wcpdf_balance_due_paid( $template_type, $order ) {
if ( $order->is_paid() ) {
?>
<div style="float:right;">
Balance due: <strong>$0.00</strong>
</div>
<?php
}
}
or a somewhat more fancy looking ‘PAID’ label:
add_action( 'wpo_wcpdf_after_order_details', 'wpo_wcpdf_balance_due_paid', 10, 2 );
function wpo_wcpdf_balance_due_paid( $template_type, $order ) {
if ( $order->is_paid() ) {
?>
<div style="float:right; display:inline-block; color:white !important; background-color:green; padding:2mm; border-radius:1mm; font-weight:bold !important; clear:both;">
PAID
</div>
<?php
}
}
If you haven’t worked with code snippets (actions/filters) or functions.php before, read this guide: How to use filters