If you have a PAF file open, you can open additional files by using Open in the File menu. You can choose which one is visible from PAF's Window screen.
You can also choose Tile Vertical to view both files at once. This is usually done in the Individual view, for a side by side comparison of the individuals in two files. This can be handy if you find an old PAF file and want to compare it to your current file.
By the way, keep several backups. (Give each a different name.) Pinning all of your hopes on one backup is the genealogical equivalent of Russian Roulette. How many recent backups are needed? At least 5 in my opinion, with at least 2 of these stored externally to your hard drive. (on flash drive or iPod, CD/DVD, supplementary hard disk, another computer on your home network, online, as an email attachment, even floppy disks if you have an older computer)