Current versions of OSX do not recognize the suffixes .FH .FH10 .FH11 … but individual programs still do as does Snow leopard / Freehand.
Make sure all your files have their suffixes visible.
For FH MX use .FH11
For FH10 use .FH10
You can type the suffix strait in to the file name
Use Get info command to reach window below:
Your files should look like this on the Host (Sierra / High Sierra)
And like this on the Guest