Perpendicular on a line segment from a given point

I want to calculate a point on a given line that is perpendicular from a given point.

I have a line segment AB and have a point C outside line segment. I want to calculate a point D on AB such that CD is perpendicular to AB.

I have to find point D.

It quite similar to this, but I want to consider to Z coordinate also as it does not show up correctly in 3D space.