You can hide the product weight from the PDF invoices, when using our free default Simple template, with this code snippet
/**
* PDF Invoices & Packing Slips for WooCommerce:
* Adds custom styles to the PDF documents
*/
add_action( 'wpo_wcpdf_custom_styles', function( $document_type, $document ) {
?>
.invoice .weight {
display: none;
}
<?php
}, 10, 2 );
However, if you have the Premium Templates extension, you only have to uncheck the Show weight option, within the Product item column block, in the customizer:
