This is simple after you have loaded PAF 5 on and I suggest you download the latest 5.2.18 you start paf and it will come up with the Starting box asked to open or search for PAF Databases. Cancel this. Then click File, Then Click Restore, it will display the restore BOX chnage the Drive at the top to A: if you have your back on on a Floppy. At the bottom where is says back type PAF5 .zip press the down arrow and the next one down is PAF 3/4 .bak slect this your backup file will be displayed. Select it and then press Restore.
PAF 5 will now restore your PAF 4 database and then convert it to PAF 5.