How to change word to pdf in c# windows form app?

Question

I have used using Spire.Doc; but it does not chnage more than 3 pages?

        private void btnSave_Click(object sender, EventArgs e)
        {
                  //initialize word object
                    document = new Document();
                    document.LoadFromFile(samplePath);

                    //Save doc file.
                    document.SaveToFile(docxPath, FileFormat.Docx);
                    //Convert to PDF

                    document.SaveToFile(pdfPath, FileFormat.PDF);
                    MessageBox.Show("pdf  ", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    document.Close();
     
        }