private async Task <string> DownloadPdfFileAsync()
		{
			var filePath = Path.Combine(FileSystem .AppDataDirectory, "CifradoEnRedes_122017.pdf");
			if (File.Exists(filePath))
			{
        		return filePath;
			}

    		var httpClient = new HttpClient();
    		var pdfBytes = await httpClient.GetByteArrayAsync("https://1drv.ms/b/s!AtMYJuNNyNicilx0lIqs4Za0F9UA?e=T8uc1V");
    		try
    		{
        		File.WriteAllBytes(filePath, pdfBytes);

        		return filePath;
    		}
    		catch (Exception ex)
    		{
        		await Application.Current.MainPage.DisplayAlert("Error", ex.Message, "Ok");
    		}

    		return null;
		}
private async  void Btn2Click(object sender, EventArgs e)
		{
			App.MasterDet.IsPresented =false;
			await App.MasterDet.Detail.Navigation.PushAsync(new DISPERSION());
			var filePath = await DownloadPdfFileAsync();

    		if (filePath != null)
    		{
        		await Launcher.OpenAsync(new OpenFileRequest
        		{
            		File = new ReadOnlyFile(filePath)
        		});
    		}
    		
		}