You can do any thing that you want to .They are you birds. BUT it is not recommended because ducks are so messy and needs lots of water to keep their nose and eyes clean. They can be pastured together but to share the water and feed, The chickens would not have clean water. Also most chickend coops have mites. Chickens dust them slef to control mites but ducks preen them self to keep the oil on their feathers.
You will do very well , with this BYC site to learn, Like I have on the does and don`t . To have a healthy flock. One of their links is very good to read.