ryanb31's suggestion about an Open method, prompted further investigation. This is the code that finally works well:
Dim xlApp As Excel.Application
Dim xlWkBk As Excel.Workbook
Dim xlWkSht As Excel.Worksheet
Set xlApp = CreateObject("Excel.Application")
xlApp.Workbooks.Open strSaveToPathAndFileName
Set xlWkSht = xlApp.Worksheets(1)
Dim ExcelLastCell As Object, iLastDataRow As Integer
Set ExcelLastCell = xlWkSht.Cells.SpecialCells(xlLastCell)
iLastDataRow = ExcelLastCell.row
Dim i As Integer
For i = 1 To iLastDataRow
If Trim(xlWkSht.Cells(i, 1)) <> "" Then
If Trim(xlWkSht.Cells(i, 8).Value) = "UNKNOWN" Then
xlWkSht.Activate
xlWkSht.Rows(i).Select
xlApp.Selection.Font.ColorIndex = 3
xlApp.Selection.Font.Bold = True
End If
End If
Next i
xlWkSht.Cells(1, 1).Select
xlApp.ActiveWorkbook.Save
xlApp.ActiveWorkbook.Close
xlApp.Workbooks.Close
Set xlWkSht = Nothing
Set xlWkBk = Nothing
Set xlApp = Nothing