Here's the final code...

Word._Application appWord = null;
Word._Document docWord = null;

Object filename = path;
Object ConfirmConversions = System.Reflection.Missing.Value;
Object ReadOnly = true;
Object AddToRecentFiles = System.Reflection.Missing.Value;
Object PasswordDocument = System.Reflection.Missing.Value;
Object PasswordTemplate = System.Reflection.Missing.Value;
Object Revert = System.Reflection.Missing.Value;
Object WritePasswordDocument = System.Reflection.Missing.Value;
Object WritePasswordTemplate = System.Reflection.Missing.Value;
Object Format = System.Reflection.Missing.Value;
Object Encoding = System.Reflection.Missing.Value;
Object Visible = false;

Object saveChanges = false;
Object originalFormat = null;
Object routeDoc = null;

appWord = new Word.Application();
appWord.Visible = false;
docWord = appWord.Documents.Open(ref filename, ref ConfirmConversions, ref ReadOnly,
ref AddToRecentFiles, ref PasswordDocument, ref PasswordTemplate,
ref Revert, ref WritePasswordDocument, ref WritePasswordTemplate,
ref Format, ref Encoding, ref Visible);
if (docWord.ProtectionType == Word.WdProtectionType.wdNoProtection)
{
docWord.ActiveWindow.Selection.WholeStory();
docWord.ActiveWindow.Selection.Copy();
IDataObject data = Clipboard.GetDataObject();
_RichTextBox.Rtf = data.GetData(DataFormats.Rtf).ToString();
}
else
{
_RichTextBox.Rtf = "";
}
docWord.ActiveWindow.Close(ref saveChanges, ref routeDoc);
appWord.Quit(ref saveChanges, ref originalFormat, ref routeDoc);