Using pcf-files is a method to transfer geometries without actually tranferring the obj-file, usually because the obj-file is copyrighted. By using a pcf-file, you make sure that the receiver must have the original obj-file in order to use your geometry. In order to decode the pcf-file, you need Objaction Mover, a utility you can find in Free Stuff here at Renderosity (do a search for "Objaction Mover"). You also need the original obj-file of course :-)