The PDF viewer is the Algori PDF Viewer Pro (v 1.0.8), by Kevin Bazira.
(A special shout-out to Kevin, who kindly helped a WordPress novice unpack and load a first WP Plugin.)

A few words on navigating the viewer:
It’s possible to simply scroll through a document, such as the Greek Alphabet chart displayed here, within the window of the viewer.
However, to read the chapters of The Starlines of Almagest, we recommend switching to fullscreen (“Presentation Mode”), by clicking on the icon with four exploding arrows. Switch from page to page using the spacebar, or the right/left arrows, to create a flipbook effect. (You’ll see what we mean once you get started.)
The viewer’s default is to open with a sidebar thumbnail view. In some instances, you might have to close the sidebar in order to see the fullscreen icon. (Don’t ask us to explain.)

The pdf displayed here may also be printed or downloaded by clicking the obvious icons beside the Presentation Mode arrows. The same is true for a number of ancillary references.
However, at this stage the chapters of the book cannot be downloaded. The plan is to solicit feedback and corrections from early readers, to create an official edited First Edition — and that edition will be made available for download.

(We want to provide readers the option of owning their own digital copy of the book.
But nobody is served by having dozens of different drafts in circulation.)