Microphone calibration files should be in text format, and could have one of a number of file extensions (.txt, .csv, …) The extension is easy to change, but the data format is less so. Here is the start of a calibration file that I received from Earthworks:
"Transfer Function Mag - dB volts/volts (0.10 oct)(eq)(eq:aux)" "Hz" "Data" 781.25, 0.7222968 820.3125, 0.7226313 859.375, 0.7241868
The first two lines are ignored, and the file will work with just the data values. You can also add a third column that contains phase information as well.