It depends on the version of Photos that you have installed, babowa.
Photos 1.0 to 3.0 and iPhoto have still the tools to create a Calendar. You can save it as a PDF, if you create a preview (Preview a print project in Photos or iPhoto to avoid issues - Apple Support).
But starting with Photos 4.0 on Mojave all tools to create a book or a calendar have been removed from Photos. we have to use the extensions to create the project, and they do not yet allow to save a PDF.
I am not happy about the new way to create projects in Photos 4.0. There are two problems. I can only work on the projects, if I am connected to the internet. That makes it impossible to work on a book or calendar, when I have time, for example, when commuting and I cannot create a PDF to share with friends and family or to enjoy in iBooks on my iPad.
Plus, the Mimeo extension keeps crashing on my Macs, perhaps it is not yet supported in Germany.