It is a 2-step process. You will need PAF4, which can be downloaded for free from www.familysearch.org (PAF 4 and 5 can both be run on the same computer so there is no need to uninstall PAF5.)
Open the DAT files from the File menu in PAF4, and allow it to convert them to PAF4 format.
Then open the PAF4 files in PAF5 and allow it to convert them to PAF5 format.
An alternative is to install the DOS version of PAF2.31 from the current PAF5 installation CD and export everything as a gedcom file, which can then be imported into newly created PAF5 files. But I would opt for using PAF4.