Uploading A World To My Pocketmine Server[Issue]

I have downlaoded a couple .mcworld/.zip worlds from some websites. I convert them to .zip and upload but everytime i load that world by doing /mw load [name] it says this is world isnt compatable and server crashes. I had once added a downloaded kitpvp map which worked well but after that it hasnt worked with any of the rest. Pls help. Thank You.

So is there a way to convert between world formats