To alter webp product image size in invoice document for mPDF add-on users - By WebToffee (WooCommerce PDF Invoice, Packing Slips, Delivery Notes and Shipping labels)

functions.php

<?php //do not copy this line of code
add_filter('wf_pklist_alter_product_table_columns', 'wt_pklist_alter_product_image_size', 10, 5);
add_filter('wf_pklist_alter_package_product_table_columns', 'wt_pklist_alter_product_image_size', 10, 5);

function wt_pklist_alter_product_image_size($product_row_columns, $template_type, $_product, $order_item, $order) {
    if ('invoice' === $template_type) {

        $image_id = $_product->get_image_id();
        if ($image_id) {
            $image_url = wp_get_attachment_url($image_id);

            if ($image_url) {
                // Use fixed width and height in pixels for mPDF compatibility
                $image = '<img src="' . esc_url($image_url) . '" width="100" height="100" style="object-fit:contain;" />';
                $product_row_columns['image'] = $image;
            }
        }
    }
    return $product_row_columns;
}