FOX - Currency Switcher Professional for WooCommerce

Plugin URL: https://wordpress.org/plugins/woocommerce-pdf-invoices/

In file wp-content\plugins\woocommerce-pdf-invoices\includes\woocommerce-pdf-invoices.php add next code:

if (class_exists("WOOCS")) {
    global $WOOCS;
    $currency = get_post_meta($order_id, '_order_currency', TRUE);
    if (!empty($currency)) {
        $WOOCS->current_currency = $currency;
    }
}