  We present results of hard X-ray angle-resolved photoemission spectroscopy
and photoemission diffraction measurements performed on high-quality single
crystals of the valence transition compound EuPd$_2$Si$_2$ for temperatures
25~K $\leq$ T $\leq$ 300~K. At low temperatures we observe a Eu $4f$ valence
$v=2.5$, % occupation number $n=6.5$, which decreases to $v=2.1$ for
temperatures above the valence transition around $T_V \approx 160$~K. The
experimental valence numbers resulting from an evaluation of the Eu(III)/Eu(II)
$3d$ core levels, are used for calculating band structures using density
functional theory. The valence transition significantly changes the band
structure as determined by angle-resolved photoemission spectroscopy. In
particular, the Eu $5d$ valence bands are shifted to lower binding energies
with increasing Eu $4f$ occupancy. To a lesser extent, bands derived from the
Si $3p$ and Pd $4d$ orbitals are also affected. This observation suggests a
partial charge transfer between Eu and Pd/Si sites. Comparison with {\it
ab-initio} theory shows a good agreement with experiment, in particular
concerning the unequal band shift with increasing Eu $4f$ occupancy.
