My question is simple is there any way to load a flight plan into the FMC of the PMDG 737 NGX?

I have seen a way to save them but no way to load them

Im not aware of a specific program that can do that, but I load my flight plan once, then save the plan as a CORoute. Next time I want to fly that route all I have to do is type in the CDU something like KMIAKTPA001, and enter it where it says CO ROUTE and the flight plan is loaded.

Absolutely you can. There is a folder: <FSX/P3d Root>/PMDG/FLIGHTPLANS/NGX. You simply generate your flight plan (I use SimBrief.com) and save it to the NGX folder in the format DEPTDEST.rte (i.e. KJFKKLAX.rte). SimBrief defaults to that format. Then simply type (for JFK to LAX example) KJFKKLAX into the COROUTE field and it will load the flight plan.

That will only load the en route portion though. You still need to manually load the SID/STAR, if applicable. 

It's been a while since I flew the NGX, but the datalink may be modeled as well (EDIT: yes, it's modeled). It's listed in the FCOM but forget if it's modeled. There is a prompt on the RTE page labeled "FLT PLN REQUEST>". Enter the ORIGIN and DEST ICAO codes and then click the LSK opposite the > (it's LSK 3R) and it will request and then load the plan. You also have the option to load performance data and winds if they are included in the .rte file (SimBrief includes that data). Just as with using COROUTE, you do still have to manually enter your SID/STAR. 

2 hours ago, adamant365 said:

You also have the option to load performance data and winds if they are included in the .rte file (SimBrief includes that data). Just as with using COROUTE, you do still have to manually enter your SID/STAR. 

The NGX does not do this,  the newer 777 and 747 do however.  The only "data link" is the flightplan load via request. 

MOD NOTE 1: NGX-related topics should be in the NGX subforum. Moved.

MOD NOTE 2: Topics should ideally be named with the actual content. Sure, this has to do with the FMC, but it also has to do with airplanes. Both titles are very broad/vague. Since this is directly related to flight plan loading, I've added that to the title to make it a bit more specific to the actual discussion.

I completely forgot about the CO ROUTE feature Brain lapse 

and thanks for clearing up the title and putting in the proper place I will pay more attention next time.

Thanks for the info.