The .pif, or Program Information File format was an attempt by Microsoft to have some kind of descriptive scripting language that could describe the environment an associated .exe or .com file should run in.
It had the ability to load dlls/drivers and to restart your machine (usually used to restart in dos mode) before running the associated program file.
It's a legacy format, used mostly in Windows 3.x, although it was also supported in Win9x and possibly newer versions.
This kind of file is ideal for computer viruses or worms.