Is docker desktop free version secure? Are the files in the containers only stored on my C drive confidentially?
Your files are not shared with anyone and will remain on your machine if this is what you mean, but Docker Desktop is for development, not for production use, and on dev machines people usually don’t store confidential data. It could happen if you have special data which would be hard to simulate with test data, but for production containers, you will need Docker CE or cluster orchestrators like Kubernetes.
Note that this is the default behavior, but you always need to check what Docker Desktop extension you enable and how that handles data. The core Docker Desktop currently don’t move any data out of your own machine.