It's not a public domain text -- the only way to get it is to buy it, either new, such as from Amazon:
Latin: An Intensive Course (Paperback)
or used, such as from alibris or abebooks:
Latin: An Intensive Course
Latin: An Intensive Course
or, of course, your local book store.
If you are looking for a free, downloadable Latin text, you might consider D'Ooge's, which available from textkit:
Latin for Beginners
as well as in a transcribed format (txt and html) from Project Gutenberg:
Latin for Beginners
The nice thing about D'Ooge is that it also has a forum here at textkit, as well as an answer key:
Latin for Beginners Key
Two other free texts you might want to consider because of their growing popularity around here are Adler's Practical Grammar and Via Nova:
Discussion of Adler's
Discussion of Via Nova