The device PeWEC (Pendulum Wave Energy Converter) developed by a partnership between ENEA and the Politecnico di Torino University, was simulated by using the open-source wave energy converter simulation tool WEC-Sim complemented by a Boundary Element Method (BEM) code for the calculation of hydrodynamic coefficients. Numerical results were compared to experimental data carried out at INSEAN laboratory tank tests. Free-decay simulations were performed numerically in order to determine the natural frequencies of the system. Moreover, a set of simulations was carried out with regular waves by varying the wave period and keeping the amplitude constant. The dynamic response of the device and the absorbed power were analysed and compared to experimental results. The code better predict the evolution of the oscillations of the pendulum rather than those of the hull but, more generally, the experimental and the numerical power curve presented good agreement. For the wave periods close the natural ones of the system, by neglecting viscous damping the absorbed power by the device is strongly overestimated by the numerical approach, while, considering this effect, an improved agreement is noticed. For the other wave periods numerical and experimental data show similar values. Finally, simulations were conducted by giving the user-defined wave elevation time-history measured by one of the probes in the test tanks. Even if mean and maximum values of the dynamic response were already well predicted, such a simulation permitted to know the dynamic of the system at any given time with a major precision. The usage of only open-source codes could provide to both industries and new WECs designers an efficient and straightforward tool to study and improve wave energy converters technology.