To update a selection in the drafts folder
Option Explicit

Public Sub AddSignature()
'Graham Mayor - https://www.gmayor.com - Last updated - 12 Apr 2021
Dim FSO As Object, oSig As Object
Dim olItem As MailItem
Dim strPath As String
Dim strSignature As String
Const strSig As String = "Graham Mayor.htm"    'the signature to add - change as required


    If Application.ActiveExplorer.Selection.Count = 0 Then
        MsgBox "No Items selected!", vbCritical, "Error"
        Exit Sub
    End If


    strPath = Environ("appdata") & "\Microsoft\Signatures\"
    Set FSO = CreateObject("Scripting.FileSystemObject")
    Set oSig = FSO.OpenTextFile(strPath & strSig)
    strSignature = oSig.ReadAll
    oSig.Close


    For Each olItem In Application.ActiveExplorer.Selection
        If olItem.Parent = "Drafts" Then
            If TypeName(olItem) = "MailItem" Then
                With olItem
                    .BodyFormat = olFormatHTML
                    .HTMLBody = .HTMLBody & strSignature
                    .Save
                End With
            End If
        End If
    Next olItem
lbl_Exit:
    Set FSO = Nothing
    Set olItem = Nothing
    Set oSig = Nothing
    Exit Sub
End Sub