woocommerce-pdf-invoices-packing-slips is an extension which allows users to create, print & automatically email PDF invoices & packing slips for WooCommerce orders. This vulnerability allows unauthorized users to access any PDF document from a store if they: 1. Have access to a guest document link and 2. Replace the URL variable `my-account` with `bulk`. The issue occurs when: 1. The store's document access is set to "guest." and 2. The user is logged out. This vulnerability compromises the confidentiality of sensitive documents, affecting all stores using the plugin with the guest access option enabled. This issue has been addressed in version 4.0.0 and all users are advised to upgrade. There are no known workarounds for this vulnerability.