PPJ projects come from some earlier version of Adobe Premiere Pro which was able to produce various multimedia files. it is not clear whenever the latest version of Adobe Premiere Pro still support .ppj file type or you need to use some of the older version of the program to perform your conversion. Anyways, it is unlikely any 3rd party software would be capable of working with .ppj projects.
Convert Adobe Premiere 6 and older video project to MPEG-4 video file format.
We found one software available in the database for this conversion.
Microsoft Windows software - convert ppj to mp4 on Windows
A timeline-based video editing software from Adobe
Convert from ppj 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.