Cannot be done. Period.
And, yes, no way to open any FMP12 file with any earlier version. It's a one-way conversion -- no going back.
About what I figured. So, how about the reverse? Can you host .fp7 files on an FM12 server? Or use the FMP12 client to open .fp7 files? I'm pretty positive the latter is not possible, but not sure about the former.
Using FMP12 client to open FM7 files converts them, and then they won't work with FM7 clients. I believe even that is possible only on unhosted files because the Servers won't host files to the wrong client versions.
So, again, not possible that way either. This really is an either/or situation with the two file formats.
okay, thanks for the helpful information!