As far as we know, it is not possible to "convert" MP4 multimedia files as PDF documents. Nonetheless, some software might allow users 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 transcription service / software can be used to produce a text from voice and eventually save it as PDF.
Open M4A file Open PDF fileGoogle Chrome extension for Google Drive