Public Sub TestMe()

    Dim wb As Workbook
    Set wb = Workbooks.Open("C:pathtesting.xlsx")
    ThisWorkbook.Worksheets(1).Range("A3") = GetSheet1A1(wb)
    wb.Close False

End Sub

Public Function GetSheet1A1(wb As Workbook) As Variant

    GetSheet1A1 = wb.Worksheets(1).Range("A1").Value2

End Function