There is probably no direct way how you could convert an M4A multimedia file to a Word DOCX document, which is what m4a to docx conversion represents.
However, you can find 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 conversions. When you get the text file with the transcription, you can easily save it as document in MS Word or similar word processor.
Unfortunately, there is no detailed software record in the database that match this conversion.
M4A
FIles with m4a extension are audio files stored in MPEG-4 (MP4) container and use AAC (Advanced Audio Coding), or Apple Lossless (ALAC) audio compression. M4A is very popular on Mac computers, because it is default audio format used by iTunes. M4A is also default audio format for Apple portable devices (iPod, iPhone, iPad).
DOCX
Files with docx file extension are documents written and saved using Microsoft Word word processor edition 2007 or later. DOCX format replaced the previously used DOC format, moving from binary files to Open XML schema-based documents. They are supported in almost every modern word-processing tools.