The spectroscopy mode of ballistic electron emission microscopy was used to study the thickness dependence of the collector current I(c) for 8-90 angstrom thick Pd films deposited on Si(111) and Si(100) substrates. The observation of similar spectral intensities for the thinnest films on both orientations is attributed to disorder induced scattering at the Pd-Si interface, which is conventionally equivalent to a breakdown of transverse momentum conservation. Fits to a model based on this interpretation give unprecedented agreement over a wide energy range. The attenuation of I(c) with film thickness exhibits strong nonexponential behavior for all tip biases studied (less-than-or-equal-to 6 V), which is due to a changing dominance among scattering mechanisms as the film thickness varies. A simple analytical expression, based on a random-walk approach, is derived that allows a unique determination of the energy dependent elastic and inelastic mean free paths of hot electrons in the Pd films.