The present work describes a new method for the surface functionalization of cellulosic sheets, overcoming the limitations of the traditional treatments, which are usually performed using fibrous suspensions. The method consists in obtaining a product (post-enzymatic) derived from an enzymatic reaction using Laccase and a compound showing a specific property. The obtained product, which has aqueous consistency, is then applied to the surface of a finished paper sheet (or cellulosic substrate) by means of impregnation, spray, size-press, or other available surface deposition technique used in the industry. The functionalization is produced by means of physicochemical interaction between the product and the substrate. In the present research, the methodology is developed to achieve the hydrophobization of finished paper sheets using Lauryl Gallate (LG) as hydrophobic compound, and a laccase derived from Trametes Villosa, reaching absorption times of up to 4000 s and CA values around 130° as assessed by the water drop test (WDT) and contact angle measurements (CA) respectively