Sub Button1_Click()
     Dim cdp, txt, strDate
     DDocALL ActiveWorkbook  
     strDate = Format(Now, "dd-mm-yy hh-mm")
     SDoc ActiveWorkbook, "Создан", "dd-mm-yy hh-mm"
      
        txt = GDoc(ActiveWorkbook, "Создан")
     MsgBox txt, vbInformation, "Пользовательские свойства книги Excel"
    
' Вместо dd-mm-yy hh-mm пробовал писать strDate  тоже не получается

Sub SDoc(ByRef WB As Workbook, ByVal VarName As String, ByVal VarValue As Variant)
        DDoc WB, VarName     
      WB.CustomDocumentProperties.Add VarName, False, msoPropertyTypeString, CStr(VarValue)
End Sub

Function GDoc(ByRef WB As Workbook, ByVal VarName As String) As String
     Dim cdp
     If WB.CustomDocumentProperties.Count > 0 Then
         For Each cdp In WB.CustomDocumentProperties
             If cdp.Name = VarName Then GDoc = cdp.Value
         Next
     End If
End Function

Function GDocB(ByRef WB As Workbook, ByVal VarName As String) As Boolean
     Dim cdp
     On Error Resume Next
     If WB.CustomDocumentProperties.Count > 0 Then
         For Each cdp In WB.CustomDocumentProperties
             If cdp.Name = VarName Then GDocB = CBool(cdp.Value)
         Next
     End If
End Function