StreamReader sr = new StreamReader(openFileDialog.FileName);
                    string html = sr.ReadToEnd();
                    sr.Close();
                    sr.Dispose();
                    mshtml.HTMLDocumentClass hdoc = new mshtml.HTMLDocumentClass();
                    hdoc.IHTMLDocument2_write(html);
                    mshtml.IHTMLElementCollection ec = hdoc.getElementsByTagName("table");

                    for (int i= 0 ; i<ec.length; i++)
                    {
                        mshtml.HTMLTableClass table = (mshtml.HTMLTableClass)ec.item(null, i);
                        foreach( mshtml.HTMLTableRowClass row in table.rows )
                        {
                            foreach ( mshtml.HTMLTableCellClass col in row.cells )
                            {
                                // если в ячейке русский текст -- ошибка!
                                MessageBox.Show(col.innerText.ToString());
                            }
                        }
                    }