I contacted ProSeries Support. I had copied the 18Data Proseries Professional file to an external hard drive.  In order to see the files in the target computer, I had to do a File, Client Maintenance, Restore.  After which I was able to see the files.

I did the same for 2017 and the program told me I could not copy 1 file, 1 will would not restore because I did not install a state (this one I installed the state and subsequently was about to restore the client). But I got a shock when I clicked EF Center and check the Accepted Tab (checking  which tax returns were accepted) and it was BLANK!  So something is not right.   Now I have to go back and check if my 2018 acceptances are all copied over!  Not as easy as it should be...

I am thinking of trying your method.  So I go to the File Explorer in the back end to copy the COMMON and HOMEBASE folders only and then paste in the target computer, using the same name - make sure no duplicate?