There's a bunch of programs that used PCF. Cisco used it for networking, It's been used for proprietary fonts, and Valve games used it to store game parts. They were also used as an image archive. Kind of like the way a PSD has layers but form the 90's and whole images. Since you said it's old I suspect this may be what you have. I've read that winzip can open them but I don't have it and WINzip.

Before you can use it you'll need to know what it was for.