The file contains only the model parameter values, for small signal operation, so this is easiest just to use this data directly in any ADS schematic. The file is not in a format that can be imported or included without alteration.
Just place a Curtice2_Model element (from the Devices-GaAs palette/library) and fill in the parameters as provided. If a parameter value is not provided just leave it empty.
Then place a GaAsFET element from the same palette/library and refer it to that model.