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sch usually is generated by SCHematic capture CAD software. The others are probably other files generated by the same software.
Often if you view the contents of these files using Notepad or similar, somewhere in that mess of weird characters/ numbers you will also find the name of the CAD package as clear as day in readable form. Try it out. If you've already found it to be Personal CAD, then there you are !!
About a free viewer - I don't know. Google is your friend.