WordApplication app = new WordApplication();
          Document doc = app.Open(@"C:\somedoc.doc");
          IEnumerator searcherator = doc.Search("crimson");
          while (searcherator.MoveNext())
          {
               SearchMatch match = (SearchMatch)searcherator.Current;
               match.Replace("red");
          }
        

          Dim app As New WordApplication()
          Dim doc As Document = app.Open("C:\somedoc.doc")
          Dim searcherator As IEnumerator = doc.Search("crimson")
          While searcherator.MoveNext()
               Dim match As SearchMatch = searcherator.Current
               match.Replace("red")
          End While