I use FS Commander 9.0 for creating and controlling my flight plans and flights; however I want to use Radar Contact for the ATC aspect of my flights.  Can the flight plans I create within FS Commander be imported into or used by Radar Contact so they work together?

If PLN's can be imported into Radar Contact, how is that done?  I have looked and haven't found a way so far.

You didn't look very hard...page 101 of the RC4 manual:

"The first button to click is either one of the two on top: normally you would use the one marked with FS200x (*.pln). If this is your first use of Radar Contact, browse to the directory where your flight plans are saved. In FS2004, this is usually My Documents\Flight Simulator files. FSX is usually the My Documents\Flight Simulator X files directory. RC remembers the path to this directory, so you have to browse only this first time. Pick the flight plan you prepared"

You have to tell FSC to export in FS format, then import that file into RC4; you can find those details on page 69 of the FSC manual:

"If you intend to load a flight plan into Flight Simulator, you check the check box . In the above screenshot it reads < Flight Simulator X>, but if you are using FS 2004 and load the FS 2004 database the same check box will read."

From your other thread, it sounds like you're using FSC gps feature; instead, you can use RC4 Copilot to fly the route for you, to include make alt adjustments. Hit Ctrl+Shift+M

It took 3 mins to find this info; I highly suggest taking a few minutes to look through the manuals before you profess the software doesn't work (your other thread).  RC4 has been used for over a decade...it works fine...