[colarris (OP)]

Can a plant pollinate itself or does it have to receive pollen from a separate plant of the same species?

[Yair Doza]

In some cases it can but it has strategies to prevent self pollination.
It might be different time of maturation of the anther and stigma, separation in location the anther further apart, mechanism of pollination that ensure the pollen stick to the pollinator only on the way from the flower.
Some plants have a molecular mechanisms of self recognition whereby the pollen of the same plant does not grow along the stigma.