Where did this file come from or what generated it?
The *.cal files that I am familiar with are Calibration files - files used to store calibration values for certain equipment. If this is what it is, you should be able to use Notepad or Wordpad to view it. Double-click on the file and select Notepad or Wordpad to open with - make sure you uncheck “Always use the selected program to open files of this type.”
If, after opening it, you see any readable text of any sort, chances are it’s a calibration file.