Before deploying a change to template-preview to return a validation error for letters that are missing the address block, we need to add the new erorr message to admin.
Some content changes have been made to other messages.
The format of the message has changed.
If PDF files have a validation error which means that they can't be
opened by PyPDF2 we would previously show the 500 status error page. We
now catch PyPDF2.utils.PdfReadErrors so that we can display a custom
error message on the notification page instead.