If using the PDF, open it in a PDF app that supports two-page view (like Adobe Acrobat, GoodReader, or Preview in “Two Pages” mode) and use a stylus or the Apple Pencil with a note-taking layer (GoodNotes, Notability).
The PDF version of Unfolding is especially useful because the book contains dozens of blank/diagram templates. In print, you’d draw on them with a pen. In PDF, you can annotate digitally (or print just those pages).
Use the SQVID to help students explore a historical event from simple (one cause) to elaborate (global factors).