There have always been third-party programs to have text read aloud in Microsoft Word (Text to Speech or TTS). Word Talk, a free program from Call Scotland is one. Read &Write Gold is a commercial product which not has text to speech but also comes with its own voices. These are all programs which are added to the Word toolbar rather than opening a document in its own window.
In the latest versions of Word, you have two options for TTS, Speak and Read Aloud. Both can be added to the Quick Access Toolbar as shown in the screenshot below. Speak and Read Aloud are underlined.
Both can use the installed system voices. The major difference is Read Aloud has a Control Panel and will highlight words that are being spoken. Reading in Read Aloud starts from the cursor position. Speak will not highlight words as they are spoken and will only read selected text.
Read Aloud can also be used in the Read View under Tools. Using it in Read View will allow access to a control panel with the standard controls plus the ability to change voices.
The video below will show both Speak and Read Aloud being added and in use.