how to convert .iba file in Pages
I have an old .iba file. How to open in Pages?
Windows, Windows 10
If you have Pages v10.2 or later, you can just open an iBooks Author .iba file with Pages and it will be translated into the .pages document format. Apple has not incorporated all of the features in Pages that exist in iBooks Author, so be prepared for substantial differences in the result.
See the following:
Open an iBooks Author book in Pages on Mac - Apple Support
Transition from iBooks Author to Pages - Apple Support