What is the doctrine of Anatta? Now does it relate to the Hindu concept of Atman?

In Buddhism, the doctrine of Anatta states
that there is no constant, permanent "self" or "soul" and that the
"self" we experience is both an illusion and a source of pain. The term comes from the
Pali words "an" (not, without) and "atta" (self, soul). It is often
mentioned in the Pali canon and, along with "Dukkha" (pain or suffering) and
"Annica" (impermanence), it is one of the three subjects for meditation that
constitute mindfulness in the Theravada and Vipassana traditions of Buddhism.

The Sanskrit equivalent of Anatta is Anatman. The Hindu doctrine of Atman is therefore
the exact opposite of Anatta, with Atman meaning "self" or "soul" and the
doctrine holding that the soul exists. The six orthodox schools of Hinduism all adhere to the
doctrine of Atman, and the contradiction between Atman and Anatta is one of the major points of
difference between Hinduism and Buddhism.