Particular text-to-speech synthesizers allow users to create audio (like a .mp3 file) with a speech from a saved text file or document, but they are usually pretty expensive. And even that will, in most cases, require manual tweaking because otherwise, the audio would not be perfect.
However, you most likely won't find a simple docx to mp3 conversion that does the job with a single click.
Free text-to-speech converter Balabolka supports the import of Microsoft Word documents and direct conversion to audio files.
Updated: January 31, 2023