This is an Application Module that is part of ISO 10303-239:2005(E) "Industrial automation systems and integration - Product data representation and exchange Part 239: Application protocol: Product life cycle support"
The ISO 10303-239:2005(E) standard can be purchased from ISO. http://www.iso.org/.
When purchased, the stepmod folder of the ISO 10303-239:2005(E) should be placed at the same level as the OASIS_R1 folder.