Sounds possibly like a PAD-file or similar a format staedily making inroads into the shareware download market, normally requires the authorised software to decrypt the files and allow installation using the recomended installer package.
other options for a .ppp file are:
Serif PagePlus. Associated Program 'Serif'
Parsons Power Publisher Project file.
Point to Point Protocol.
Punk Production Picture. Associated Program 'XnView'
Picture Pump Project file.
Enfocus Preflight Profile.
Complete details can be found here:
http://filext.com/detaillist.php?extdetail=PPP