Login to your Google account and open a document.
While editing a document, press play or use the hotkeys to activate the reading. Or, use the Read Selection icon to only read from specific portions of the text.
While in 'View Only' mode, highlighting is deactivated but you can still follow along through the CC Panel in the Reading Bar.
You can also read from Sheets or Forms while in 'Edit in Google Sheets/Forms' mode only. Use Read Selection to highlight and listen to the text.