This requires the existence of the external program cpdflin which is provided with commercial versions of cpdf. This must be installed as described in the installation documentation provided with your copy of cpdf. If you are unable to install cpdflin, you must use -cpdflin to let cpdf know where to find it:
In extremis, you may place cpdflin and its resources in the current working directory, though this is not recommended. For further help, refer to the installation instructions for your copy of cpdf.