  The protoplanetary system HD 169142 is one of the few cases where a potential
candidate protoplanet has been recently detected via direct imaging. To study
the interaction between the protoplanet and the disk itself observations of the
gas and dust surface density structure are needed. This paper reports new ALMA
observations of the dust continuum at 1.3\,mm, $^{12}$CO, $^{13}$CO and
C$^{18}$O $J=2-1$ emission from the system HD 169142 at angular resolution of
$\sim 0".18 - 0".28$ ($\sim 20\,$au$ - 33\,$au). The dust continuum emission
reveals a double-ring structure with an inner ring between $0".17-0".28$ ($\sim
20 - 35\,$au) and an outer ring between $0".48-0".64$ ($\sim 56 - 83\,$au). The
size and position of the inner ring is in good agreement with previous
polarimetric observations in the near-infrared and is consistent with dust
trapping by a massive planet. No dust emission is detected inside the inner
dust cavity ($R \lesssim 20\,$au) or within the dust gap ($\sim 35 - 56\,$au).
In contrast, the channel maps of the $J=2-1$ line of the three CO isotopologues
reveal the presence of gas inside the dust cavity and dust gap. The gaseous
disk is also much larger than the compact dust emission extending to $\sim
1'.5$ ($\sim 180\,$au) in radius. This difference and the sharp drop of the
continuum emission at large radii point to radial drift of large dust grains
($>$ \micron-size). Using the thermo-chemical disk code \textsc{dali}, the
continuum and the CO isotopologues emission are modelled to quantitatively
measure the gas and dust surface densities. The resulting gas surface density
is reduced by a factor of $\sim 30-40$ inward of the dust gap. The gas and dust
distribution hint at the presence of multiple planets shaping the disk
structure via dynamical clearing (dust cavity and gap) and dust trapping
(double ring dust distribution).
