iPad file IO

So I've got to the stage where I can get the application I'm working on to the iPad for testing. The problem is though, I can't write to a data file from the iPad. In Unity I write and modify the data file fine. But I'm unable to do so on the iPad. It seems to be reading from the file fine but I can't edit the file. ie save changes to the file. The file is located at ...Data/Raw/filename.txt. Is this where the file should be placed so it can be manipulated??

Any help would be appreciated.