automatically add date to filename when saving a word document?

There is no way to do this without macros.

Take a look at Save Versions Add-In for one of the better macro solutions.

You specified without macros. I'm tossing one out, anyway.

The following macros, if placed in your document will append a date to whatever is in the Title Property. Note, no provision is made for more than one version in a day.

These should run automatically whenever the document is saved.

To see what to do with a macro, see Graham Mayor's Installing Macros.

Sub FileSave()
    ' Run as substitute for FileSave to add date to document title

    '    for filename

    ' Put in a document or document template

    '    but probably not in a global
    '
    On Error Resume Next
    '
    Dim strName As String, dlgSave As Dialog
    Set dlgSave = Dialogs(wdDialogFileSaveAs)
    strName = ActiveDocument.BuiltInDocumentProperties("Title").Value

    '    get name in title
    strName = strName & " " & Format((Year(Now() + 1) Mod 100), _

        "20##") & "-" & _
        Format((Month(Now() + 1) Mod 100), "0#") & "-" & _
        Format((Day(Now()) Mod 100), "0#")
    With dlgSave
        .Name = strName
        .Show
        
    End With
End Sub

Sub FileSaveAs()
    Call FileSave
End Sub