Adding data to a closed workbook

Yes - you can use ADO to write to a closed workbook. You haven't given any details to work with so here's a generic example:

Sub ExportDataFromThisWorkbookToClosedWorkbook()
' Sample demonstrating how to export data from the current workbook to a closed workbook
    Dim cn As Object
    Dim strQuery As String
    Set cn = CreateObject("ADODB.Connection")
    With cn
        .Provider = "Microsoft.ACE.OLEDB.12.0"
        .ConnectionString = "Data Source=" & ActiveWorkbook.FullName & ";" & _
                            "Extended Properties=""Excel 12.0;HDR=Yes;"""
        .Open
    End With
    strQuery = "INSERT INTO [Sheet1$] IN '' [Excel 8.0;Database=C:\ADO Dest.xls] SELECT * FROM [Sheet1$B2:F3]"

    cn.Execute strQuery
    cn.Close
    Set cn = Nothing
End Sub