pykd.dll is useful if you have installed pykd as a python package ( by the command 'pip install pykd') but you are going to use pykd with windbg. In this case you can copy pykd.dll to windbg winext catalog and pykd.dll will find and load pykd.pyd.
pykd.dll has two usefull additional command:
It is equal to command 'pip install pykd' - pykd will be upload and installed
It is eqal to command 'pip install --upgrade pykd'