public static void EncryptWithPassword(string unEncryptedWordPath, string password) { Word.Application wordApp = null; Word.Document document = null; try { object missung = System.Type.Missing; object odocPath = unEncryptedWordPath; object opassword = password; wordApp = new Word.Application(); document = wordApp.Documents.Open(odocPath); document.Password = password; document.SaveAs(ref odocPath, Word.WdSaveFormat.wdFormatDocumentDefault); } catch (Exception e) { string s = e.ToString(); Console.WriteLine(s); throw; } finally { Quit(wordApp, document); } } public static void Quit(Word._Application wordApp, Word._Document doc) { if(doc != null) ((Word._Document)doc).Close(Word.WdSaveOptions.wdDoNotSaveChanges); object ofalse = false; //ref false to prevent the Word Process Hang in Task Manager if(wordApp !=null && wordApp.Application != null) ((Word._Application)wordApp.Application).Quit(ref ofalse, ref ofalse, ref ofalse); }