PIT Operator (cert. ~14 months) attempted to place a pallet of product on the end of a trailer when the dock door was only approximately halfway open. When sliding the pallet onto the end of the trailer, the operator struck and damaged the bottom section of the dock door. In addition, site personnel attempted to work on the damaged dock door themselves. While doing so, the tensioning support cable was inadvertently released, causing the dock door to fall shut and the cable to fly into the air. N o injury. Cost of damage TBD.