Error while doing page count

Retrieving the COM class factory for component with CLSID {000209FF-0000-0000-C000-000000000046} failed due to the following error: 80070005 Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))

else if (extension == ".DOC" || extension == ".doc" || extension == ".docx")
                                {

                                    Microsoft.Office.Interop.Word.ApplicationClass WordApp = new Microsoft.Office.Interop.Word.ApplicationClass();
                                    

                                    // give any file name of your choice. 
                                    string tempath = numberofpage;
                                    RegexOptions options = RegexOptions.None;
                                    Regex regex = new Regex(@"[ ]{2,}", options);
                                    tempath = regex.Replace(tempath, @"");
                                    tempath = tempath.Replace(" \\", "\\");
                                    object fileName = tempath;
                                    object readOnly = false;
                                    object isVisible = true;

                                    //  the way to handle parameters you don't care about in .NET 
                                    object missing = System.Reflection.Missing.Value;
                                    object objDNS = Microsoft.Office.Interop.Word.WdSaveOptions.wdDoNotSaveChanges;

                                    //   Make word visible, so you can see what's happening 
                                    //WordApp.Visible = true; 
                                    //   Open the document that was chosen by the dialog 
                                    Microsoft.Office.Interop.Word.Document aDoc = WordApp.Documents.Open(ref fileName,
                                                            ref missing, ref readOnly, ref missing,
                                                            ref missing, ref missing, ref missing,
                                                            ref missing, ref missing, ref missing,
                                                                ref missing, ref isVisible);

                                    Microsoft.Office.Interop.Word.WdStatistic stat = Microsoft.Office.Interop.Word.WdStatistic.wdStatisticPages;
                                    count = aDoc.ComputeStatistics(stat, ref missing);

                                    WordApp.Quit(ref objDNS, ref missing, ref missing);

                                    aDoc = null;

                                    WordApp = null;

                                    GC.Collect();

                                }