What is the difference between dockerd and com.docker.service in Docker for Windows?
dockerd is a persistent process that manages containers. Docker uses different binaries for the daemon and client. ( from Docker site ). Docker Daemon is a server which interacts with the operating system and performs all kind of services. The Docker Daemon listens for REST API request and performs the operation. Its process running on the background.

Docker service is the utility we use when we run any docker commands e.g. docker run (docker container run), docker images, docker ps etc. It allows us to run these commands which a human can easily understand.