I save the previous form and the current form as doc file and then I use the Word functionality. Do you have another solution to comparing two forms with richtext fields?
The comparing result I save this as mht file to view the changes also in a browser.
Here is sample code:
object currentFile = currentDoc;
object compFile = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) + "\\" + compareFileName;
object fileFormat = Word.WdSaveFormat.wdFormatWebArchive;
object missing = Missing.Value;
object objTrue = true;
object objFalse = false;
object compareTarget = Word.WdCompareTarget.wdCompareTargetNew;
object saveChanges = Word.WdSaveOptions.wdDoNotSaveChanges;
Word.Application wordApp = new Word.ApplicationClass();
wordApp.Visible = false;
Word.Document oDoc = wordApp.Documents.Open(ref currentFile, ref objFalse, ref objFalse, ref objFalse, ref missing, ref missing, ref objFalse, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing, ref missing);
oDoc.Compare(backupDoc, ref missing, ref compareTarget, ref objFalse, ref objFalse, ref objFalse, ref objTrue, ref objTrue);
Word.Document compDoc = wordApp.ActiveDocument;
compDoc.SaveAs(ref compFile, ref fileFormat, ref objFalse, ref missing, ref objTrue, ref missing, ref objFalse, ref objFalse, ref objFalse, ref objFalse, ref objFalse, ref missing, ref missing, ref missing, ref missing, ref missing);
compDoc.ActiveWindow.View.Type = Word.WdViewType.wdWebView;
oDoc.Close(ref saveChanges, ref missing, ref missing);
wordApp.Visible = true;