Two files make up a Cimatron NC post processor.
The Df2 fie is the compiled post
The Dx2 file is for configuration settings the post can reference.

The default folder for these files is in the Cimatron install path - C:\program files\3D systems\Cimatron\14.0\Data\IT\var\post2

*NOTE: Post processor files can actually reside anywhere on the PC or the server, as long you communicate this to Cimatron in the GeneralNC preference.
See the line to set the GPP2 folder.