You're loading a file from the same server, so there's no need to use
WebClient
at all. Just use:
string filePath = Server.MapPath(Path.Combine(folder, name));
Response.ContentType = "application/pdf";
Response.TransmitFile(filePath);
The issue of the file not appearing is nothing to do with your server code; it's a browser issue. Try loading the file on a real mobile device. If it still doesn't work, then there's a problem with your file.