There is probably no direct way how you could convert an MPEG-4 audio files (.m4a) to a Word document (.doc,. docx) , which is what m4a to doc conversion likely represents. However, there do exist services that can convert the voice from an audio file and save the transcript as a text file. For this please refer to the m4a to txt conversion. When you get the text file with the transcription, you can easily save it as document in MS Word or similar word processor.
Updated: April 18, 2017