How can I move a photobook from one catalog to another, i.e. how can I export/import photobooks (not as a pdf but as a Lightroom book layout)? I only found the possibility to export the collection the book is based on as a catalog, but this catalog does not contain the book layout, only the pictures. Thanks!
In the Collections panel, right click the (saved) book and choose Export This Collection as a Catalog. This includes everything about the book, so photos, pages, page text and other customisation. It'll also include other collections, if any of the book's photos have been added to them.
In general though, LR works better as a single catalogue.