Share books and bookmarks between all devices
Using iBooks with iCloud makes this very easy.


Make sure you have an active iCloud account and are signed in on both macOS and iOS.
Open iBooks (if asked enable iCloud for iBooks).
Select File > Add to library, and add any external .epub or .pdf files
iBooks will automatically sync them to other iOS/macOS devices, including notes and bookmarks.


If you have a seperate iCloud and AppStore Apple ID. Go into iBooks preferences and check "Sync: Sync bookmarks, highlights and collections across devices", you might get a warning to change Apple ID's. Change it to your AppStore Apple ID. Even though your using iCloud to sync, it still needs the other ID.