Error -- Object variable or With block not set

I receive an Object variable or With Block not set error sometimes when running the following code:

Function wordConversion(sFileName As String)
If wordApp Is Nothing Then
Set wordApp = CreateObject("word.Application")
End If

Set wordDoc = wordApp.Documents.Open(sFileName)

<<this is where the error gets highlighted>>
With Documents.Application.Selection
.WholeStory
.Font.Name = "Ariel"
.Font.Size = 9
End With
ActiveDocument.PageSetup.Orientation = wdOrientLandscape
sFileName = nameChange(sFileName)
ActiveDocument.SaveAs sFileName, wdFormatDocument
ActiveDocument.Close

Set wordDoc = Nothing

End Function

Any ideas why this error would occur only occasionally, and how to correct the problem?

Thanks

You get that "Object variable or With Block not set" error if the Documents.Application.Selection does not return any object. I don't know how to use word in vb but so I don't know but I think this Selection will return nothing if there isnt anything selected.