You will need the actual *.csp file on order to open it with cscape.
The *.pgm is generated via the "export to removable media" and it is used to load the program to a cscape controller in the field using the MicroSD card and through the controller configuration screens.
Thus it is smaller in size as it is the compiled code.
I don't know of a way to import the *.pgm to cscape/
Of course, I may be wrong.
Your best bet is to contact their support people.