A composite film includes a polyester film substrate layer and a crosslinked layer on a surface thereof, wherein the crosslinked layer includes a reaction product of a) a functionalized ethylene vinyl acetate copolymer including multiple COOH groups or multiple alcoholic OH groups per molecule; and b) an organic crosslinker including multiple reactive groups per molecule, the reactive groups being reactive with the COOH or alcoholic OH groups; wherein the adhesion strength between the substrate layer and the crosslinked layer is at least 177 g/cm (450 g/inch). A method of joining the composite film, optionally further including a heat-sealable polymer layer on the crosslinked layer, to a container or a self-supporting film, includes contacting the crosslinked layer or the heat-sealable polymer layer with the container or the self-supporting film or under heat sealing conditions.