title: Opening a file by UIDocumentInteractionController
body: <p>I am using <code>UIDocumentInteractionController</code> for opening documents in my app. I have used method below for previewing the PDF file:-</p>
  
  <pre><code>- (IBAction)previewDocument:(id)sender 
  {
      NSString *filePath = [[NSBundle mainBundle] pathForResource:@"sample" ofType:@"pdf"];
  
      // Initialize Document Interaction Controller
      self.documentInteractionController = [UIDocumentInteractionController interactionControllerWithURL:[NSURL fileURLWithPath:filePath]];
  
      // Configure Document Interaction Controller
      [self.documentInteractionController setDelegate:self];
  
      // Preview PDF
      [self.documentInteractionController presentOptionsMenuFromRect:down.frame inView:self.view animated:YES];
  
  }
  </code></pre>
  
  <p>I have read that we can read files in an app from other app too by <code>UIDocumentInteractionController</code>.</p>
  
  <p>In my app, How can I read the files from other app using <code>UIDocumentInteractionController</code>? How does all this happens?</p>