Porting to Windows Store syntax problems

im porting a game from pc to Windows store and have alot of file operations like read and write.

when replacing the old code with the new Windows store specific code containing Windows.System.FileIO, Windows.Storage.StorageFolder, async functions etc.

unity sees this as unknown syntax...

its not something that stop the build process but will it give me other complications later on ?

is it only some of the new Windows syntax thats supported ?