PDF invoices – You have no document types enabled.

Hi, I have set up pdf invoices and under ’email options’ set ‘Attach PDF to emails’ to new order, refunded order, completed order and customer invoice / order details
When I go into one of my orders under the PDF section it is saying ‘you have no document types enabled’
Can you help?
I want to be able to download the customer invoice and packing slip from the order dashboard. And I want to email the customer a copy of the invoice when the order is completed