Macro open file and go back

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I would attempt to do something like this.

Sub Open_File()
 Dim WBSrc As Workbook
 Dim WBDest As Workbook
 Dim sFil As String
 Dim sTitle As String
 Dim sWb As String
 Dim iFilterIndex As Integer
 On Error GoTo err_handler
 Set WBSrc = ThisWorkbook
 ' Set up list of file filters
 sFil = "Excel Files (*.xls),*.xls"
 ' Display *.xls by default
 iFilterIndex = 1
 ' Set the dialog box caption
 sTitle = "Select File to Zip"
 ' Get the filename
 sWb = Application.GetOpenFilename(sFil, iFilterIndex, sTitle)
 If sWb <> False Then
    Application.ScreenUpdating = False
    Set WBDest = Workbooks.Open(Filename:=sWb)
    WBSrc.Activate
    Application.ScreenUpdating = True
 End If
 Exit Sub
err_handler:
 MsgBox "No selection made"
 
End Sub

This assigns your workbooks to variables so when you refer to them, you will always be assured that any references will be to the correct workbook. You don't have to worry which workbook is actually activated.