Hello Everyone!
If you're trying to add a free PDF to your cart and encountering an error today know we're actively working to resolve the issue and hope to have it fixed as soon as possible.
This appears to be caused by a data state where PDFs are added to your shopping cart before you sign into the website. If you sign in, remove the PDFs from your cart and then try readding them from the product page it should let you automatically add them to your My Downloads section where they can be accessed.
Thank you for your patience while we work to address this!
- Erik K