Where should I get a license key for use NVENC (H264) on Quadro K4000?

I try to use nVidia NVENC (hardware H264 encoder) on nVidia Quadro K4000, which supports it: https://developer.nvidia.com/nvidia-video-codec-sdk

The programming guide says: https://developer.nvidia.com/sites/default/files/akamai/cuda/files/CUDADownloads/NVENC_VideoEncoder_API_ProgGuide.pdf

2. SETTING UP THE HARDWARE FOR ENCODING
2.1 Opening an Encode Session

After loading the NVENC Interface, the client should first call NvEncOpenEncodeSession to open an encoding session. The NVENC Interface will provide a encode session handle to the client, which must be used for all further API calls in the current session.

2.1.1 Using the License client Key GUID:

The client should pass a pointer to the key GUID that has been delivered with this SDK or has been purchased as part of a license separately, as NV_ENC_OPEN_ENCODE_SESSION_EX_PARAMS::clientKeyPtr

Where should I get a license key for use NVENC (H264) on Quadro K4000?