I created a HUD using new UI in Unity 5. I want to display that HUD in all levels.

I created Pause button, restart button and other HUD elements using new UI. And I created a Public function for button click actions. Now I want HUD to display in all my levels.

You can use DontDestroyOnLoad to prevent objects from being destroyed when changing scenes. Use this with your canvas objects, and other objects related to your UI, and they will stay as they are no matter what scene you load during runtime.