帮忙看下这几句代码有什么错误

Question

Word.ApplicationClass myWordApp = new Word.ApplicationClass();
Word.Document MyDoc;
Object Nothing=System.Reflection.Missing.Value;
object isVisible = true; 
object readOnly = false;
object filename = @"d:\Temp\111.doc";
MyDoc=myWordApp.Documents.Open(ref filename,ref Nothing,ref readOnly,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref Nothing,ref isVisible,ref Nothing);
this.textBox1.Text = MyDoc.Paragraphs.Last.Range.Text;
未将对象保存到对象实列