I only have the .key presentation file and cannot ask the author to export it to ppt nor do I have an Apple computer available.
Since it is a proprietary format, you will need to use KeyNote to open it.
You obviously can't export the file as anything since you would need to open it first in order to export it ;-)
I know that Keynote files can be "played" in QuickTime on a Mac, but I don't know how feasible that is in Windows. Worth a try.
Creating an apple account is free and Key note is also free to use with that on ICloud. So we just needed to go to https://www.icloud.com create a user, log in with that and we have the abilities online on the browser