I want to use same functions of photon pun in playfab

>> Can I use playfab as a same service of photon pun? I don't know what exactly playfab is. Server hosting? or just solutions for game?

PlayFab provides both back-end service and a server hosting service Multiplayer Server. Backend as a service is the main business of PlayFab, most functions of Playfab revolve around it.

About the server hosting service PlayFab Multiplayer Server, it would not be the same with PUN. I’m not so familiar with Photon PUN, but as far as I know, PUN integrates some out-of-the-box network synchronization methods in its SDK package, PlayFab Multiplayer Server only provides a separate server hosting service attached corresponding API and matchmaking services. You basically need to implement all the game logic of a game server yourself. For example, integrate a third-party network framework with your server to implement the corresponding network features, such as network synchronization. Besides, we provide PlayFab GSDK on several platforms(such as C#, C++, Java, and Unity), you need to integrate the GSDK to the server before you deploy it on PlayFab. For more detailed information, please check our documents via the links above.

>> Because photon's ccu is very expensive so I'm considering changing it to playfab. Is it possible?

You can check the Pricing page for our billing plan for PlayFab developers. But if you want to use PlayFab server hosting service, you need to billing for it separately. Multiplayer Server would charge for usage of VM rather than CCU. You can check this doc Billing for PlayFab Multiplayer Servers 2.0 for more details. For a summary, you can use PlayFab back end service for free, but cannot use PlayFab server hosting service without paying.