From the publisher's website:
Aachen 1944: Germany Invaded is a supplement for the Panzer Grenadier series. There are ten scenarios, or separate game situations, based on the battles of October 1944 between divisions of the United States First Army driving onto German soil and those of the German Seventh Army desperately trying to keep them out of the Reich. This module is not playable by itself, but requires ownership of our Cassino '44, Road to Berlin, Battle of the Bulge and Elsenborn Ridge games.
It introduces German Volksgrenadiers.
Aachen 1944 is sold BOTH via .pdf download and as a printed booklet, you only need one. The scenario book comes as a .pdf file that you'll need to print (or read off the screen) in order to play the scenarios, OR you can order it as a booklet that we'll ship to you.