IDF files are used by Energy Plus to process dynamic simulations. This article details how to obtain the IDF file from OpenBuildings.
An IDF file can be obtained be obtained upon running a Dynamic Simulation in OpenBuildings Energy Simulator.
This file will be generated automatically and can be obtained from the projects Workset folder, within the Output > Results > Simulation folder:
If you are unsure of your project / Workset location please see here.