Just a little feedback to close this thread. (I'm the OP.)
Based upon your inputs, and on my faith in TurboCAD as a quality product, I didn't even try the trial version. I just plunged ahead and purchased the Deluxe, to replace my old defunct v. 4.
After my first tour through the tutorial, my first reaction was, oh my, this was a big mistake. This is so much more complicated than my old v. 4 that I will never find the time to be able to learn how to use it.
Well then, after a couple of days of starting to get a feel for, and actually using it, I have changed my mind completely. v. 18 is far smoother and user friendly than my old v. 4. And indeed, as you have said, it reads my old v. 4 files. So I am sold! It is nice to be current again, after so many years!
Thanks again for your help!