Methods, apparatus and system for decorating plastic articles having an uneven surface or hollow structure are disclosed. An assembly comprising a transfer pad and a flexible heat transfer die comprising a thermal interface material (TIM) replace the hard rubber die in a hot-stamping process to fuse indicia into the surface. The assembly modifies ordinary pad printing into a hot-stamping process that transfers indicia onto uneven surfaces. A pad printing machine or other robotics is used to move the assembly from a position of heating to a position of compressing the ink transfer to the surface of the article.