From the introduction:
End of Autumn is an adventure intended for three to five 5th-level characters using the Open Gaming License (OGL) system--the same utilized by Paizo’s Pathfinder system as well as by the 3.5 edition of the world’s most popular role-playing game.
This adventure has some elements of horror, although most GMs will find it possible to integrate into any conventional fantasy campaign. In order to run this adventure, you will need the Pathfinder Core Rule Book and the first volume of the Pathfinder Bestiary.
End of Autumn takes place within a single area of forests, hills, marshes, farmland and village, surrounding the shallow, slow-flowing Wandering River. The area could be placed in almost any larger setting: Any small area off the beaten path will do.