A family of Microsoft word processing software products for creating web, email, and print documents.
Select all the text and then (re-)apply the correct language via the Language dialog box (Review tab > Language group > Language > Set Proofing Language). In the dialog box, also disable the "Detect language automatically" option, if it is currently selected.
I also recommend that you modify the language of the Normal style (because it is the "parent," or based-on style, for many other paragraph styles in Word).