There exist a special voice search and transcription software that could capture the words from an audio file (like AAC) and save it as text, or document. Usually requires manual editing though to flesh out the errors, which are somewhat unavoidable.
Convert Advanced audio coding stream to Simple text file.
We have found one software suitable in our database for this conversion.
On-line services software - convert aac to txt on web
A Voice Search & Transcription Platform
Convert from aac file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.