This contribution presents the study of acoustic effects occurring in polymer films irradiated by high-intensity focused ultrasound (HIFU), when the films are sandwiched between a solid waveguide transducer and a solid counterpart. Whereas the heating of polymer plates induced by HIFU was already reported in the literature, the acoustic effects in thin polymer films remain not fully understood. In order to investigate the sound field occurring in polymer films, measurements of the acoustic pressure in water between transducer and counterpart spaced from 1 mm are carried out using a membrane hydrophone. The measurements are compared to an acoustic finite element simulation modeling the sound field in water between the transducer and the counterpart. In order to evaluate the analogy between the acoustic pressure measured in water and the effective acoustic pressure occurring in polymer films, a second acoustic finite element simulation is conducted to model the irradiation of polymer films with HIFU in dry environment and compared to the simulation and measurements of the acoustic pressure in water. A direct correlation between measurements and simulation is found. The investigation reveals that complex interferences occur in polymer films. These findings are relevant for new joining processes of polymer based on HIFU.