A family of Microsoft word processing software products for creating web, email, and print documents.
Press Ctrl+A to select the entire document. Open the Language dialog (Review | Language | Language | Set Proofing Language) and make sure that the "Do not check spelling or grammar" box is not checked. If it is filled, you will need to click twice to clear it. I also advise clearing the option to "Detect language automatically," which generally causes more problems than it solves.