Cannot open .gz and .dd files

I have a disc that has a .gz and .dd files on it. I have tried opening it using bitzipper and winzip but I've had no luck. Can some one help me and maybe explain the steps that are needed to be taken. thanks

GZ sounds like Gunzip. Try the program "7zip", it opens just about everything and is free.

Freearc an open gz. ExtractNow says it can but I have seen it fail.