  $\rm{PtSe_2}$ is a van der Waals material transitioning from an indirect
bandgap semiconductor to a semimetal with increasing thickness. Its absorption
threshold has been conjectured to originate from interband indirect
transitions. By quantitative comparison between broadband ($0.8 -
3.0\,\rm{eV}$) optical absorption of high-quality exfoliated crystals and DFT
ab-initio simulations, we prove instead that the optical absorption arises only
from direct transitions. This understanding allows us to shed light on the
semiconductor to semimetal transition and to explore the effect of stacking and
excitons on the optical absorption.
