Open AppleWorks and then go to the File menu and choose Open.
Navigate to the place where the .WPD file is.
Set the AppleWorks open file dialoge box to look at ALL Files. (not just Appleworks files)
The .wpd file should be available for you to choose.
Do so and click Open. See what happens. It "may" work, AppleWorks sometimes surprises us.
Another method is to use the trial version of Word that is on your Mac Mini to open the documents and to save them in .rtf format. Any word processor will open that type of file.
Just changing the extension will NOT help you, but you already knew that.
Let us know how you get on
In trying to transfer documents and such from Windows Millenium using Corel Word Perfect to AppleWorks 6 on my mini mac, I have no way to get from .wpd to .ckw, for example. Is there some free method of doing so?