On macOS, you can directly copy your annotations.
Open your annotations in the book, expand all chapters, click the first note and shift click the last note, right click and chose copy (works in Big Sur), or use Mail (this works in Mojave).
Now you can paste them into Obsidian.
On iOS (tested in 14.1), you can open your notes, touch the share icon, chose “Edit notes”, “select all”, and mail them to you. (This includes some formatting, though.)
Hope this helps!