Insert PDF in database c#

I think you should write

private void Button2_Click(object sender, EventArgs e)   //Save pdf in database
{
    OpenFileDialog ofd = new OpenFileDialog() { Filter = "PDF|*.pdf" };//Open pdf file
    if (ofd.ShowDialog() == DialogResult.OK)
    {
        FileStream fs = File.OpenRead(ofd.FileName);
        MemoryStream ms = new MemoryStream();
        fs.CopyTo(ms);
        using (SqlConnection openCon = new SqlConnection(cs))
        {
            if (openCon.State == ConnectionState.Closed)
                openCon.Open();
            string saveStaff = "declare @maxNo integer = 0 select @maxNo = isnull(max(number), 0) from [dbo].[documents]; Set @maxNo=@maxNo+1; INSERT into dbo.documents (number,file_location, pdf_file) VALUES (@maxNo,@file_location,@pdf_file)";
            using (SqlCommand querySaveStaff = new SqlCommand(saveStaff))
            {
                querySaveStaff.Connection = openCon;
                querySaveStaff.Parameters.Add("@file_location", SqlDbType.VarChar, 255).Value = file_locationTextBox.Text;
                querySaveStaff.Parameters.AddWithValue("@pdf_file", SqlDbType.VarBinary).Value = ms.ToArray();
                querySaveStaff.ExecuteNonQuery();
            }
        }
    }
}

You can use FileStream to read a pdf file, then copy pdf data to MemoryStream. To save pdf to your database, you only need to convert MemoryStream to byte array.