MP3 audio files typically cannot be directly converted to Microsoft Word formats (.doc, .docx) and it is extremely unlikely that you can´find some mp3 to word document converter. Nevertheless, when you are working with documents in Microsoft Word, you have an option to import OLE objects, which includes MP3 audio. This option will essentially embed MP3 file on one of the page in the document.
Some mp3 tag editors offer users a way to export embedded information from mp3 song (album covers, lyrics etc.) and save the information as text that can be imported (copy + paste) to MS Word, which is what mp3 to doc conversion might also refer to.
Another potential type of mp3 to word conversion might be audio to text conversion in which users seek a tool capable of audio transcription. Such task can be usually done with programs or services like VoiceBase.Open MP3 file Open DOC file