If you accept "This is in the textbook," why not also "That is in the textbook?" Really, if we were conversing in English about something I would say "that" rather than "this." You will probably respond that Russian has "тот" but if it's not common use? I think the most commonly used translation should at least be accepted. It is literally a different word, but everybody knows literal translations are not the best.
Yes, Petrenko has it right. Also, if for example a CD is included with the book, you could say "it comes with the textbook"; but probably not "in." This is a likely answer to the question, where did you get the CD. Otherwise, you would probably say "The textbook comes with a CD."