Ebooks

What type of eBook and for what platform was it intended? PDF? ePUB, Kindle, Other?

An eBook intended for the Kindle should use the latest Kindle app from the Mac App Store. If it is a PDF, then open it in Apple's Preview application. If it is a regular eBook (ePUB) it may open in Apple's Books application.

There is the macOS Kindle app for Amazon eBooks.

There is the Apple Books app for Apple Store eBooks.

Barnes & Noble only supports mobile phone eBook readers, but you can read books you purchased from Barnes & Noble via web browser from the B&N web site.

If your eBook if in ePub format, Apple's Books app can read it.

PDF files can be read using Preview app

RichText ebooks can be read using TextEdit app.

So as VikingOSX asks, what format is your ebook, or where did you get your ebook from?