Got it figured out.....on Plesk, both the key AND cert are in one file called httpd.pem located under the user's cert directory. It's simple to do, ssh in to the cert you need, copy it and paste it into the box provided under DA....and DA handles the rest.
Yes, the private key and certificate are both in the file named httpd.pem. I copied and pasted the entire file into the text area provided by DA on the certificate pages.....DA actually separates the key and cert into 2 files....