How to open a downloaded file

I am writing an application for Xamarin.iOS, but an answer in native iOS would suffice. After I download a file (image or pdf) I want to open it:

public void DidFinishDownloading(NSUrlSession session, NSUrlSessionDownloadTask downloadTask, NSUrl location)
    // how to open location?

I tried UIApplication.SharedApplication.OpenUrl(location); but nothing happens.

Source: Xamarin.ios Questions