To open last modified file from a folder:

Const myDir = "H:\Test\backup-stephen's workbook"
Sub GetLatestFile()

Dim fso As Object
Set fso = CreateObject("scripting.filesystemobject")
Dim fil As Object
Dim myFolder
Dim myFilename As String
Dim dateOfFile As Date


'set up initial folder
Set myFolder = fso.GetFolder(myDir)


'To loop through each file and get date last modified. If largest date then store Filename

dateOfFile = DateSerial(1900, 1, 1)
For Each fil In myFolder.Files
If fil.DateLastModified > dateOfFile Then
dateOfFile = fil.DateLastModified '  this is the important logic
myFilename = fil.Name
End If
Next fil
Workbooks.Open myFilename

Set FileSys = Nothing
Set myFolder = Nothing
End Sub