(Ni₈₃Fe₁₇)_1-x-Gd_x thin films (30 nm) are deposited by sputtering at room temperature and studied using X-ray diffraction, vibrating sample magnetometer, and ferromagnetic resonance (FMR). The film structure changes from polycrystalline to amorphous when Gd content is around 5.7%. The magnetization is reduced almost linearly with the increase of the Gd content, while the high hysteresis squareness along the in-plane easy-axis, the low coercivity H_c of less than 10 Oe, and the high maximum permeability of around 1000 are all preserved. Theoretical fitting of angular dependences of FMR field yields the second and forth order perpendicular anisotropy constants K_perp1 and K_perp2 which show a spin reorientation with increasing Gd doping. The FMR linewidth is fitted by considering the contributions from Gilbert damping and inhomogeneous broadening. It is found that the damping coefficient alpha is tripled along with an enhancement of the gyromagnetic ratio gamma when the Gd content rises to 9.3%.