However, it is worth noting that while PDFs are convenient for personal reference, the full value of the book is unlocked through active participation—physically folding paper, drawing stick figures, and completing the problem sets.
The PDF layout often uses a quadrant diagram to explain these four actions: Unfolding The Napkin Pdf
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). However, it is worth noting that while PDFs