What energy conversions take place in a pendulum?
Conversion of Kinetic into Potential Energy (and vice-versa).
When you move the bob of the pendulum to start the movement you "charge" it with (Gravitational) Potential Energy by varying its position (height) in relation to the ground. When you release the bob it moves towards the equilibrium position changing Potential into Kinetic Energy (through the movement with Velocity). At the equilibrium point the bob doesn't stop but goes on up to the same height "re-charging" it with Potential Energy.
The sum of Kinetic
All this if you can neglect Friction otherwise at each swing you lose energy and at a certain point all the initial energy will be changed, say, into, other forms of Energy (Internal Energy, for example, heating up the point of suspension of the pendulum).