The stove must never be operated with the door open, the door should only be fully opened when you need to refuel your fire. Smoke may be emitted into the room at the time of refuelling if the stove is burning at a very low rate.
To overcome this, you can either burn your fuel at a much hotter temperature, or you can open the door slightly (1 or 2 cm) for a few minutes before adding any additional fuel.
If the door is left open for too long whilst you're refuelling your stove, then a large amount of cool air will be drawn into the chimney, chilling the flue gases and slowing the draw of your stove. This will result in smoke and fumes coming back into the room, therefore the refuelling time should be kept to a minimum.
If smoke is persistent, and the stove is difficult to light and maintain a good burn rate, then there may be a problem with the chimney draught. In this case, you should consult your installer or a qualified chimney sweep.