To view a full-sized PDF of a chapter or save the chapter, you’ll want to open your book in Atticus and click on the chapter you'd like to view:
Click the preview option at the bottom of the right hand side bar and change the preview form the default iPad view to Print
Give it a moment to render your book then click on the page in the preview
This will open up that chapter alone in a PDF in your browser, so you can view the full size PDF of this chapter there or save it to your computer.