Thanks for reaching out! Sorry for the late reply.
Unfortunately, PathFinder doesn't allow you to copy the file (window) path in POSIX format now.
I am forwarding your message to our developers as a feature request.
Though you can always (manually) get file path by right-clicking it and choosing Copy Path.
Also, you can right-click the Path Line. We support exporting the path in UNIX, HFS, Windows, Terminal and URL formats.
I hope this helps. Please feel free to write us back and we will be happy to assist you.