  The possibility that a relevant fraction of the dark matter might be
comprised of Primordial Black Holes (PBHs) has been seriously reconsidered
after LIGO's detection of a $\sim 30 M_{\odot}$ binary black holes merger.
Despite the strong interest in the model, there is a lack of studies on
possible cosmological implications and effects on cosmological parameters
inference. We investigate correlations with the other standard cosmological
parameters using cosmic microwave background observations, finding significant
degeneracies, especially with the tilt of the primordial power spectrum and the
sound horizon at radiation drag. However, these degeneracies can be greatly
reduced with the inclusion of small scale polarization data. We also explore if
PBHs as dark matter in simple extensions of the standard $\Lambda$CDM
cosmological model induces extra degeneracies, especially between the
additional parameters and the PBH's ones. Finally, we present cosmic microwave
background constraints on the fraction of dark matter in PBHs, not only for
monochromatic PBH mass distributions but also for popular extended mass
distributions. Our results show that extended mass distribution's constraints
are tighter, but also that a considerable amount of constraining power comes
from the high-$\ell$ polarization data. Moreover, we constrain the shape of
such mass distributions in terms of the correspondent constraints on the PBH
mass fraction.
