There is one PDF file I have in my Books app that I would like to keep permanently on the device and not to have to download in from iCloud when I want to access it, can someone tell me how I do that?
I'm not sure with the Books iCloud setting enabled that you can do that. An alternative would be to save that PDF in the Files app in your On My [device] storage, open it, select the share sheet and tap on Books to read it in that app.