  Associated production of bottomonia and open charm hadrons in $pp$ collisions
at $\sqrt{s}=7$ and $8$TeV is observed using data corresponding to an
integrated luminosity of 3$fb^{-1}$ accumulated with the LHCb detector. The
observation of five combinations, $\Upsilon(1S)D^0$, $\Upsilon(2S)D^0$,
$\Upsilon(1S)D^+$, $\Upsilon(2S)D^+$ and $\Upsilon(1S)D^+_{s}$, is reported.
Production cross-sections are measured for $\Upsilon(1S)D^0$ and
$\Upsilon(1S)D^+$ pairs in the forward region. The measured cross-sections and
the differential distributions indicate the dominance of double parton
scattering as the main production mechanism. This allows a precise measurement
of the effective cross-section for double parton scattering.
