A family of Microsoft word processing software products for creating web, email, and print documents.
The application can be hidden but not individual document windows. Most likely the document window is Minimized.
If so there should be an icon at the right end of the Dock which you can click to restore the window or go to the Window menu in Word & select the document by name. Other options are to just click the Word icon in the Dock or right-click it & select the document by name or select Show All Windows.