No 'add note' in Books app

Hello,

I am sure it's probably user error, but I have followed the steps for adding a note to my book, in the books app, and no "add note" option pops up. There is a small menu, that does allow me to highlight, but no way to add a note.

Could this be because it's a pdf of a textbook? Or am I missing something?

Thanks for any help!