Is it possible to export an IBooks Author file to Pages?
iMac with Retina 5K display, iOS 11.4.1
Not really. You would have to copy/paste the text from one app to the other, or do File > Export > Text and then open that with Pages.
A good workflow is to start with Pages. That lets you export tontwo different types of ePub, Pdf, and you can always pull the Pages file into iBooks Author (multi-touch or ePub template) for iBooks Author in case you need to add widgets not available in Pages.
Plus you can’t export as PDF from iBooks Author ePub templates.
How can I export an IBooks Author file to Pages?
