switch (extension)
        {
            case "DOCX":
                options.ContentType = "application/vnd.ms-word.document.12";
                break;
            case "EXCEL":
                options.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
                break;
            case "PPT":
                options.ContentType = "application/vnd.openxmlformats-officedocument.presentationml.presentation";
                break;
            case "PDF":
                options.ContentType = "application/pdf";
                break;
        }

        await Windows.System.Launcher.LaunchUriAsync(uri, options);