Steve is exactly right. You'll have to save the version 7 file as a version 5 in order to open it in ver 5.

Open the file in 7 click save as in the file menu. A window will open and to the right side of the window will be a drop down window which identifies the version. You click on the version you want.

By default when you open files in V. 7 it will save them as v.7 files unless you go through the process to save them as v.5.

Mike Null
Dist. of Lazer Cutting Grid
www.stl-laser.com