Adobe Premiere Pro projects (.prproj files) can be exported to many video formats, including MPEG-4 (.mp4) which is the obvious choice how to convert prproj to mp4 format. Just keep in mind that these projects do not contain multimedia audio of its own, just settings and references that are used to generate the output. Which means that without the relevant multimedia data, prproj to mp4 conversion will be impossible.
Open PRPROJ file Open MP4 file