A novel maize variety designated PHCD4 and seed, plants and plant parts thereof. Methods for producing a maize plant that comprise crossing maize variety PHCD4 with another maize plant. Methods for producing a maize plant containing in its genetic material one or more traits introgressed into PHCD4 through backcross conversion and/or transformation, and to the maize seed, plant and plant part produced thereby. Hybrid maize seed, plant or plant part produced by crossing the variety PHCD4 or a trait conversion of PHCD4 with another maize variety. Inbred maize varieties derived from maize variety PHCD4, methods for producing other inbred maize varieties derived from maize variety PHCD4 and the inbred maize varieties and their parts derived by the use of those methods.