I m assuming that you want to hear Word Documents since you posted on this
site.
Windows Narrator is a basic screen-reading program. It offers speech
feedback in a variety of situations (i.e. all menus and dialog boxes, Windows
Explorer and Notepad) but will not speak in some parts of most applications
(i.e. a Word document or web page). It can be set to echo your keystrokes
(this will work in all situations).
from: http://www.abilitynet.org.uk/myway/language/talk/windows-narrator.htm