A turbofan might look like an enclosed turboprop, but the way they create thrust is different.
Turboprops use the props to create "pull" force (like wings create a lift force). The pull force is there from speed 0 to max speed by altering the pitch angle. This "pull" force is primarily created because the prop rotates, not because the aircraft moves forward. Therefore very efficient at low speeds, but limited because of propeller tip speeds when the aircraft does start to increase its speed.
Turbofans create thrust by displacing a huge amount of air. Therefore less efficient at low speeds since the engine has to suck the air into itself, but more efficient at high speeds where the forward speed of the aircraft already pushes huge amounts of air into the engine (and where the inlet already creates a compression).
Another evolution in between is the geared turbofan, which uses pitch control to control the amount of air displaced by the fan. Today this is done by controlling engine RPM (fan is fixed pitch). For higher thrust you need to accelerate the engine as well, which makes it "sluggish", slow in reaction time. A turboprop is already at high RPM, therefore thrust control through pitch control is very quick in reaction times at all regimes. The geared turbofan displaces huge amounts of air to create thrust, and thrust control is done through pitch control (quick reaction).
Turbojets create thrust by taking a lower amount of air compared to the turbofan, but accelerating it more (hence less propulsive efficiency).