If I am reading your message correctly, it appears that you are trying to have PAF 5 convert your BACKUP files from PAF 4. PAF 5 will not be able to convert a backup file. You will need to re-install PAF 4, restore your backup files into PAF 4, then you can have PAF 5 convert those ".paf" files.
Even though PAF 5 will convert those files for its use, your PAF 4 data files will still be there as well. Just make sure you save the new PAF 5 data to a new folder and don't overwrite the old PAF 4 data files.