Here's a short explanation of the differences between the text to speech features in Office and Windows.
Read Aloud Read Aloud reads all or part of a document. It starts reading at your cursor position, and will continue until it runs out of text, or you shut it off. While running, Read Aloud disables AutoSave. If you had AutoSave on, it will enable it when Read Aloud is done. Read Aloud is available only in Office 365 subscriptions. For more info, see Listen to your Outlook email messages or Listen to your Word documents with Read Aloud.
Speak Reads only the text that you've selected. For more info, see Use the Speak text-to-speech feature.
Narrator Narrator is the Windows Screen reader app that reads you dialog boxes, buttons, and other user interfaces. For more info, see Using Windows Narrator in Office for the web.