CERN-LHCb. 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. $\Upsilon$ mesons are recontructed using $\Upsilon \to \mu^+ \mu^-$ decay mode, while for charm hadrons $D^0 \to K^- \pi^+$, $D^+ \to K^- \pi^+ \pi^+$, $D^+_s \to K^- K^+ \pi^+$ and $\Lambda_c \to K^- \pi^+$ decay modes are used.