Normally if you double click on a GEDCOM file from any source it will automatically import into your Family Tree Maker.
Alternatively, start your Family Tree Maker, File menu, Close Family File. Then File menu, Open Family File, click the Files Of Type box, and select GEDCOM. Navigate in the Look In box to the folder where the GEDCOM is saved. Select the GEDCOM, and open it.
If none of that works, you may e-mail me the GEDCOM and I will check it out.