Abstract: The method provides the protection or personalization of the pre-printed sheets by impressing microengravings, on all or some of the printed portions of the sheets, through an embossing process carried out on the pre-printed sheets at a temperature higher than the softening point of the dyeing substances used for obtaining the print thereon and followed by a cooling step, said microengravings corresponding to holograms or diffraction patterns or images or words.

Abstract: A method for impression microengravings, which reproduce holograms, kinetic holograms, or diffraction patterns, directly on paper through an embossing process. Paper is subjected to a humidification step to give it a degree of humidity between 60 and 80% of relative humidity. The humidified paper is then passed through an embossing group, consisting of an embossing cylinder carrying the microengravings and a counterthrust cylinder, at a temperature and a pressure on the paper within the ranges of 90-220.degree. C. and 20-120 kg/mm.sup.2, respectively.