It is not possible to "convert" MP4 multimedia files as PDF documents. However some programs may allow you to embed an MP4 file to a PDF document which can then be played when the PDF is viewed. Though Flash is the preferred content for PDFs nowadays and not just any multimedia files.
Also a transcription service / software may be used to produce a text from voice and eventually save it as PDF.
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).
PDF
A pdf file extension is mainly used for Adobe Portable document format, commonly referred to as PDF. All programs that create some sort of documents or projects offer the possibility to export their format to PDF format. A free PDF viewer (Adobe Reader) is available for download from Adobe website.