Press the speaker icon in the set or summary bar. A natural voice reads only the text, including formulas and signs such as minus, spoken in words; it skips maps, quizzes, flashcards and image captions. Press again to stop it.
The first time you listen to a document you pay 1 credit; for the next 30 days listening again is free on that device. If the audio doesn't start, the credit is returned. Pro feature.