openFileDialog1.Filter = "PDF files (*.pdf)|*.pdf";

            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                string fileName = openFileDialog1.FileName;
                System.IO.FileInfo fi = new System.IO.FileInfo(fileName);


                // Document metadata.
                #region metadata
                File file = new File(fileName);
                Document document = file.Document;
                //...