Copy file from iOS 11 Files app to sandbox

I want to copy a file from the iOS 11 Files app to my local app sandbox. For testing purposes it is assumed that the file is locally available in the Files app (downloaded from iCloud to the local storage). The file extension is registered with my app and when a file is pressed in the Files app then my app receives the file URL from the Files app:

NSFileCoordinator *fileCoordinator = [[NSFileCoordinator alloc] initWithFilePresenter:nil];

NSURL *nsUrl; // comes from Files app. For instance "file:///private/var/mobile/Library/Mobile%20Documents/com~apple~CloudDocs/test.rar"
NSURL *targetUrl; // file in my app's document directory

NSError *coordinatorError = nil;
[fileCoordinator coordinateReadingItemAtURL:nsUrl options:NSFileCoordinatorReadingWithoutChanges error:&coordinatorError byAccessor:^(NSURL *newURL) 
{   
    NSFileManager *fileManager = [NSFileManager defaultManager];
    //if ([fileManager fileExistsAtPath: [nsUrl path]])
    {
        NSLog(@"Copy from %@ to %@", newURL, targetUrl);

        NSError *copyError = nil;
        [fileManager copyItemAtURL:newURL toURL:targetUrl error:&copyError];
        if (!copyError)
        {
            // OK
        }
        else
        {
            NSLog(@"Files app error: %@", copyError);
        }
    }
}];

But the operation fails with this output:

2017-11-22 09:30:28.685127+0100 test[434:40101] Copy from file:///private/var/mobile/Library/Mobile%20Documents/com~apple~CloudDocs/test.rar
 to file:///var/mobile/Containers/Data/Application/01BB33E6-2790-0FD0-8270-000/Documents/test.rar
2017-11-22 09:30:28.687174+0100 test[434:40101] Files app error: Error Domain=NSCocoaErrorDomain Code=257 "The file “test.rar” couldn’t be 
opened because you don’t have permission to view it." 
UserInfo={NSFilePath=/private/var/mobile/Library/Mobile Documents/com~apple~CloudDocs/test.rar, 
NSUnderlyingError=0x1c084abf0 {Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"}}

Is there something special required to get read access to the external file?

Regards,

Here is how you can access the files and stop when are done with it.

//To gain access
[nsUrl startAccessingSecurityScopedResource]

and

//To stop access
[nsUrl stopAccessingSecurityScopedResource]