You can preview any certificate you've made or are making at any point using the PDF button. You can do this from the Certificate tab or from within the certificate.
On the Right hand side you will see a button that says PDF, if you click this at any point it will generate a Certificate for you to view.
From within the Certificate you are editing you can also do this using the button in the Tools menu
The red PDF button here will generate a PDF at any point in time. Depending on if the Certificate is finalised, you will get either a Sample PDF or a Completed one with an individual Certificate number shown in the example below.