A family of Microsoft word processing software products for creating web, email, and print documents.
Use Ctrl+A to select all the text, then go to the Language dialog and make sure that "Do not check..." is not checked (you may have to click twice to completely clear the check box). It's also advisable to disable "Detect language automatically," which usually causes more problems than it solves.
For more on spell checking, see http://wordfaqs.ssbarnhill.com/MasterSpellCheck.htm