While Pressbooks can't import directly from Pages, we can offer a few tips for how to bring your book into Pressbooks effectively.
1. Copy/pasting your content. Paste each chapter into Pressbooks individually. As long as you paste into the Visual Editor, any Pages formatting that is supported in Pressbooks will be retained in your content. Note that if you paste your content into the Text Editor your formatting will be lost.
2. Importing your content. Pages offers the ability to export your Pages document as a Word document. After you've done this, you can import the .docx file into Pressbooks using the Word Importer tool.
For more information on how to import from Word, check out our user guide: https://guide.pressbooks.com/chapter/import-from-word-docx/