Hi Nurali,
You will get the count like below.
Microsoft.Office.Interop.Word.Application word2 = new Microsoft.Office.Interop.Word.Application();
Document doc2 = new Document();
object missing = System.Type.Missing;
object fileName2 = @"D:\Documents\ SecondExample.doc";
doc2 = word2.Documents.Open(ref fileName2, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing,
ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
int count = doc2.Sentences.Count();