It appears that ppr to mp4 conversion is related to export of ProShow Producer projects (.ppr) to MPEG-4 videos (.mp4), something that can be only done using the original software. Projects typically do not contain multimedia data, just references to them.
Convert ProShow Producer project to MPEG-4 video file format.
We found one software available in the database for this conversion.
Microsoft Windows software - convert ppr to mp4 on Windows
A software used to create professional slideshows
Convert from ppr 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.