C # operate word bookmarks

Word. Application app = new Word. Application ();
// Template File
String TemplateFile = @ "D: \ lin \ Invoice.doc ";
// Generate a new file with a template Style
String FileName = @ "D: \ lin \" + DateTime. Now. ToString ("yyyyMMddHHmmssfffffff") + ". doc ";
String Fname = DateTime. Now. ToString ("yyyyMMddHHmmssfffffff") + ". doc ";
// FileName = Server. MapPath ("~ /UpLoad/TestWord/"+ Fname );
// Copy the template file to the new file
File. Copy (TemplateFile, FileName );
Word. Document doc = new Word. Document ();
Object Obj_FileName = FileName;
Object Visible = false;
Object ReadOnly = false;
Object missing = System. Reflection. Missing. Value;
// Open the file
Doc = app. Documents. Open (ref Obj_FileName, ref missing, ref ReadOnly, ref missing,
Ref missing,
Ref missing, ref Visible,
Ref missing,
Ref missing );
Doc. Activate ();

Foreach (Word. Bookmark bm in doc. Bookmarks)
{
If (bm. Name = "BookMark_Date ")
{
Bm. Select ();
Bm. Range. Text = "2008"; // ViewState ["FK_ProdurcePlanID"]. ToString ();
}
// Else if (bm. Name = "class ")
//{
// Bm. Select ();
// Bm. Range. Text = ViewState ["_ class"]. ToString ();
//}

}
Object IsSave = true;
Doc. Close (ref IsSave, ref missing, ref missing );

Response. Write ("<script language = 'javascript '> alert ('word generation successful! '); </Script> ");