Hello Kyle you are right.
1)..PMDG sent me an external activation http://downloads.precisionmanuals.com/file_library/PMDG_777_200LRF_Activation.zip
2)..Unzip to the root folder same folder your fsx.exe file is located, this is important otherwise it wont work.
3)..Run the PMDG_777_Activation exe file :"VERY IMPORTANT"if you are running Vista,7, or 8 run as admin otherwise it wont work
4)..Enter your licence key. i found that when i tried a couple of times it did not work it only worked after i install PMDG777 under the repair mode
5)..Active the product
Hope this helps
Terry