The Professional electronic edition comes as a personalized
high-quality PDF file that can be read, searched, annotated, and printed.
You may keep separate copies on all your computers and devices simultaneously, and
print as much of the book and as often as you like – including the
entire book. There is no opening password or watermark; only the PDF's metadata are personalized.
The cross-references in the text are active links: when a proof cites
"Lemma 3.1", for example, click on the "3.1" to be taken to that
lemma. For each result or proof, there are links in the margin to
take you to the results needed for this proof, or in whose proof the
current result is used.
The Professional edition includes free upgrades to all future editions of the book. In the iOS version, you can also download past editions for free, and buy translations.
If you would like to print handouts for a course you are teaching
from the book, you can get your Department to obtain a licence for
that too; see here for details.