There is not a way that I know of to compare more than two documents at a time, onscreen side by side.
If you have multiple revision documents you can combine them into one new document, but you probably are already aware of that feature.
If you have multiple revision documents and you want to "automate" the process a bit to cut down on some of the manual input you have to do, you can use a macro like the one below.
Sub CompareDocs()
Dim doc As word.Document, iDoc As word.Document, rDoc As word.Document
Dim selFiles() As String, strFolderPath As String
Dim Sep As String, i As Long
On Error GoTo errHandler
Sep = Application.PathSeparator
Set doc = ActiveDocument
Application.ScreenUpdating = False
With Application.FileDialog(msoFileDialogFilePicker)
.Title = "Select the files to compare to your source document"
.InitialFileName = curDir
.AllowMultiSelect = True
If .Show = 0 Then
Exit Sub
End If
ReDim Preserve selFiles(.SelectedItems.Count - 1)
strFolderPath = Left(.SelectedItems(1), InStrRev(.SelectedItems(1), Sep))
For i = 0 To .SelectedItems.Count - 1
selFiles(i) = .SelectedItems(i + 1)
Next
End With
For i = 0 To UBound(selFiles)
Set iDoc = Documents.Open(selFiles(i))
Set rDoc = Application.CompareDocuments(OriginalDocument:=doc, RevisedDocument:=iDoc, _
CompareFormatting:=False, CompareComments:=False)
rDoc.SaveAs2 strFolderPath & "Compared_" & iDoc.Name
rDoc.Close
iDoc.Close
Next
Application.ScreenUpdating = True
MsgBox "Document Compares Complete"
Exit Sub
errHandler:
MsgBox Err.Description, vbCritical, "Compare Docs"
Err.Clear
Application.ScreenUpdating = True
End Sub