You can do this either by using paths or NSURLs. Apple recommends using NSURLs, so here’s how it works.
In this example we’re copying a file called “Amy.png” which exists in the app’s main bundle.
// file URL in our bundle
NSURL *fileFromBundle = [[NSBundle mainBundle]URLForResource:@"Amy" withExtension:@"png"];
// Destination URL
NSURL *destinationURL = [[self applicationDocumentsDirectory]URLByAppendingPathComponent:@"Amy.png"];
// copy it over
[[NSFileManager defaultManager]copyItemAtURL:fileFromBundle toURL:destinationURL error:nil];