Save PDF to a C # directory

Good afternoon everyone, looking for your support to be able to save a PDF file in a selected directory, I have the following method in which I can already see the directories and select the file, if someone can tell me how to solve it, in advance Thanks for your help.

private void btnGuardar_Click(object sender, EventArgs e)
{
    try
    {
        SaveFileDialog objSave = new SaveFileDialog();
        objSave.Filter = "Archivos de texto (*.pdf)|*.pdf|Todos los archivos (*.*)|*.*";               
        objSave.Title = "Seleccione un PDF";
        objSave.ShowDialog();
        if (objSave.FileName != "")
        {
            System.IO.FileStream file = (System.IO.FileStream)saveFileDialog1.OpenFile();
            switch (saveFileDialog1.FilterIndex)
            {
                case 1:
                    this.btnGuardar.
                    //this.btnGuardar.Image.Save(file,
                    //   System.Drawing.Imaging.ImageFormat.Jpeg);
                    break;
            }
            file.Close();
        }
    }
    catch (Exception ex)
    {
        ex.ToString();
    }
}