Files in Books open like documents do in Finder. Additionally, files in Finder cannot open with Books. This is a problem for a Mac mini with macOS Ventura 13.1. with a 3 GHz 6-Core Intel Core i5 processor.
Mac mini, macOS 13.1
pdfs in the Books app will always open in whatever pdf reader you have selected ie Preview. You can control click a file in finder to open in Books ie import it, but it will still open in Preview.
Two things. I switched the default pdf reader to Books from info using the lock or right-click, that produced dialogue box error saying Books can't open the file, but when changing it to Finder, right-click only opens the Books app, it still couldn't open the pdf.
The pdf I changed to open with Books by default, whether right-clicking or double-clicking, produced an error box saying it can't be opened because it is from an unidentified developer.
I tried it with pdf files on hard drive, also iCloud storage.
Books open in Preview app
