As another user already mentioned, Simbrief is free to create your own flight plan and then export to a PMDG flight plan for loading in the FMS. Usually you’ll need to manually add the SID and STAR procedures, but this only takes a second. If you want the latest AIRAC cycle on the PMDG, this will require a Navigraph subscription. Simbrief does allow you to select a historical AIRAC for routing.
I’m not sure why you’re making your life more difficult by doing this manually, but there is a free and easier option.