If you want to use a file you've created with the PFM Editor with minidrivers, you'll need to convert the file using the CVTHPPFM utility. You run this utility from the MS-DOS̉ command line.
Additionally, if you want to convert 3.1 PFM files to use with 3.0 PFM files, you can use the CVTHPPFM utility to perform this conversion as well.