Help opening a .dat game exe file to a readable version?

i want to open a 7.28gb dat file which is a game it should be all the folders(programs saves ect) however the person i downloaded it from said they opened it with wordpad when i try it says it is too big for word pad, and every other program i try it comes up as scribbles i have tried the following: wordpad, notepad, mircosoft word, winzip, winrar, adobe reader ,and windows media player can somone please tell me a program that can either open aa large dat file or change a large dat file to somthing i can open