Sub CopyPasteSaveSelection()
On Error GoTo ErrTrap

Dim rngToCopy As Range
Dim twb As Workbook
Dim nwb As Workbook
Dim app As Excel.Application
Dim lngLastRow As Long
Dim sh As Worksheet

With Application: .ScreenUpdating = False: .DisplayAlerts = False: .EnableEvents = False: End With

Set twb = ThisWorkbook
Set sh = twb.Sheets(2) 'If sheets are not supposed to be moved around it is better to use index. If sheets are not supposed to be renamed it is better to use names.
Set rngToCopy = Selection

lngLastRow = sh.Range("A" & Rows.Count).End(xlUp).Row
sh.Range(Cells(lngLastRow + 1, 1).Address, Cells(lngLastRow + rngToCopy.Rows.Count, rngToCopy.Columns.Count).Address) = rngToCopy.Value

Set app = New Excel.Application
app.Visible = False
Set nwb = app.Workbooks.Open("c:\temp\test.xlsx")

lngLastRow = nwb.Sheets(1).Cells(Rows.Count, 1).End(xlUp).Row
nwb.Sheets(1).Range(Cells(lngLastRow + 1, 1).Address, Cells(lngLastRow + rngToCopy.Rows.Count, rngToCopy.Columns.Count).Address) = rngToCopy.Value

nwb.Close True
Set nwb = Nothing
Set app = Nothing

With Application: .EnableEvents = True: .DisplayAlerts = True: .ScreenUpdating = True: End With

Exit Sub
ErrTrap:
    MsgBox "En error occured while processing the data. Please contact support. CopyPasteSaveSelection: " & Err.Number & " " & Err.Description
End Sub