Normally a Mistral saved calculation file, Eg. #.awc, #.cwc, #.lwc etc., when double clicked.
However there are circumstances under some Windows Operating System conditions and which are outside of Mistral's control where they will not open by this method.
The solution is to either create a new folder under the Mistral program installed program path (typically C:\Program Files (x86)\Mistral) and move the files into the new folder, or, if fearful of doing due to Windows illogical warning messages discouraging this then simply copy these calculation files into C:\Program Files (x86)\Mistral\Sample Calculations folder (changing C: if your hard disc drive letter is different).
Windows will protest with unwarranted warning messages but these can generally be ignored.
See also:- AWC or CWC double clicking fail