Of course, 3-phase alternating current can be converted into a rippling direct current with a 3-phase bridge rectifier.
This design only draws current from the two phases with the most voltage differential at any given moment. Therefore, even with a constant load on the DC side, the current drawn from each line doesn't resemble a sine wave, but each phase is at zero current most of the time.
Is there a type of 3-phase to DC power converter that draws current from each phase roughly proportional to voltage, so that the current drawn from each resembles a sine wave? I imagine that such a converter would work by switching between pairs of phases, but I'm not aware of an existing design that does this.