UIWebView not displaying .rtfd.zip files

Question

I have an app with a UIWebView and a UITableView. The UIWebView displays an .rtfd.zip file with the same name as the selected table row. I use this code:

NSString* sourceFilePath = [[NSBundle mainBundle] pathForResource:[self title] ofType:@"rtfd.zip"];
NSURL* url = [NSURL fileURLWithPath:sourceFilePath isDirectory:NO];
NSURLRequest* request = [NSURLRequest requestWithURL:url];
[webview loadRequest:request];

but UIWebView displays just a blank page (all the outlets are properly connected). Where is the problem?

Thanks in advance!