I have a WebClient created in a WebBrowser_Navigating event handler. It stops navigation (to prevent manual filedownload dialog) and passes the referred URL to the webclient's DownloadFileTaskAsync method.
await client.DownloadFileTaskAsync(e.Url, AppDomain.CurrentDomain.BaseDirectory + "\\SUCCESS.pdf");
I have already set the SecurityProtocolType to Tls12 and passed all cookies and other headers to the webclient.
The file expected is about 11 MB large.