Corelx7 and x8

Hi all I am looking for some serious help, I have just had x7 on a 1 month free trial and after it expired they offered me x8 for 16 days free. I am now worrying because a lot of my original work was done in x7 but then I opened it and made changes in x8, so here's my problem I was looking at just buying x7 because it's gives me everything I need at the present time but if I do buy it will I still be able to open all the saved files in x8 or will I lose them because x8 is a newer programs.??? I don't want to commit until I know fully. Can somebody help me out.