let
    Source = Folder.Files("C:\Users\user\Desktop\Новая папка (5)"),
    #"Added Custom" = Table.AddColumn(Source, "a", each let
    Source = Excel.Workbook([Content], null, true),
    Sheet1_Sheet = Source{[Item="Sheet1",Kind="Sheet"]}[Data],
    #"Promoted Headers" = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"a", Int64.Type}, {"b", Int64.Type}, {"c", Int64.Type}})
in
    let  a = _[Name] in Table.AddColumn( #"Changed Type","Источник",  (_)=> a)
),
    Custom1 = Table.Combine( #"Added Custom"[a])
in
    Custom1