Does anyone know if there's anyway to print an existing Photos book project into an actual book now that Apple has discontinued their printing service?  I know Mimeo Photos and others have jumped in to fill the printing void with a Photos extension, but as far as I can tell, you must start completely over with a new project using their layout interface.

I know you can save a given Apple Photos book project to a PDF, but then is there any service that will take a PDF and make it into a book?