Method for protecting printed data on a varnish area of a transfer film of a heat-transfer machine, including: a varnishing step during which the varnish area and a plastic card advance simultaneously under the thermal head and during which the thermal head heats in order to deposit the varnish on the plastic card, generating a deformation of the transfer film at a text printed on the plastic card; a rewinding step during which the transfer film is rewound in order to position the varnish area upstream of the thermal head, and the plastic card is repositioned upstream of the thermal head; and a defacing step during which the varnish area and the plastic card advance simultaneously under the thermal head and during which the thermal head heats at the level of the text and at the deformation in accordance with a sign scheme making the deformation illegible.