A novel hybrid maize variety designated X0842K and seed, plants and plant parts thereof, produced by crossing an inbred maize line with a Pioneer Hi-Bred International, Inc. proprietary inbred maize line. Methods for producing a maize plant that comprises crossing hybrid maize variety X0842K with another maize plant. Methods for producing a maize plant containing in its genetic material one or more traits introgressed into X0842K through backcross conversion and/or transformation, and to the maize seed, plant and plant part produced thereby. This invention relates to the hybrid seed X0842K, the hybrid plant produced from the seed, and variants, mutants, and trivial modifications of hybrid X0842K. This invention further relates to methods for producing maize lines derived from hybrid maize variety X0842K and to the maize lines derived by the use of those methods.