Where Can I Legally Buy the North American Digital Edition of CS:APP 3rd Edition?

A legitimate North American eText does exist. Try searching VitalSource by ISBN 978-0134092997, which is the eText ISBN for the North American 3rd edition. The corresponding print ISBN is 978-0134092669. Pearson also lists a lifetime Pearson+ eText under ISBN 978-0138105396, so searching by ISBN is much more reliable than searching only by the book title.

The advice to avoid the Global Edition is mainly about the exercises and their solutions, not because the core explanations of computer systems are unrelated. For casually learning the concepts, the Global Edition may be adequate, but I’d choose the North American eText if the price difference is reasonable and you want dependable exercises, matching page references, and compatibility with course materials.

The Global Edition isn’t completely different—the main textbook chapters are largely the same, so it can still be useful for reading and self-study. However, the exercises are an important distinction. The Global Edition uses a different set of practice and homework problems, and the authors’ errata information warns that those problems and solutions contain numerous errors. If you plan to complete the exercises or follow a course based on the North American edition, the original edition is the safer choice.