Loop a macro through the multiple files

    Set wkbCsv = Application.Workbooks.Open(Filename:=strFOLD & strFile)

Originally Posted by shg

    Set wkbCsv = Application.Workbooks.Open(Filename:=strFOLD & strFile)

Yes. It works. Thank you.
There is another problem.
My original recorded macro can do the work completely for one file, but I can not put Step 5 in the loop in polished version of macro (next code).

'Step5: Inserting FileName as "ID" in ColA until the last row of data
         
     Range("A2").Select
     ActiveWorkbook.Names.Add Name:="ID", RefersToR1C1:="=GET.DOCUMENT(88)"
     ActiveWorkbook.Names("ID").Comment = ""
     ActiveCell.FormulaR1C1 = "=SUBSTITUTE(ID, "".csv"", """")"
     Range("A2").Select
     
     Dim Lr     As Long
     Lr = Cells.Find("*", , , , 1, 2).Row
     If Selection(1).Row < Lr Then
        Selection.AutoFill Destination:=Selection.Resize(Lr - Selection.Row + 1)
     End If
     

This one is the polished one. The step 5 is not included in this code.

Sub Macro_data_L3()

    ' Set folder containing CSV files
    Const strFOLD As String = "C:\Users\test\New folder\"
    
    ' Set formula to be used
    Const strFORMULA As String = "GET.DOCUMENT(88)"
    
    Dim strFile As String
    Dim wkbCsv As Workbook
    Dim lngLastRow As Long
    
    strFile = Dir$(strFOLD & "*.csv", vbNormal)
    
    Do While strFile <> vbNullString
        Set wkbCsv = Application.Workbooks.Open(Filename:=strFOLD & strFile)
        
        With wkbCsv.Worksheets(1) 'step1: Deleting 1st row
            .Rows("1").Delete
            
            With .Columns("B")
                .Clear
                .Insert
            End With
    'Step2: TXT2Col
            .Columns("A").TextToColumns _
                Destination:=.Range("A1"), _
                Other:=True, _
                OtherChar:=Chr(47), _
                FieldInfo:=Array( _
                    Array(1, xlGeneralFormat), _
                    Array(2, xlGeneralFormat), _
                    Array(3, xlGeneralFormat))
     'Step3: Changing cell format to DMY
            .Columns("A:C").ClearFormats
            .Range("A1:C1").Value = Array("Day", "Month", "Year")
     'Ste4: Swapping Columns
            .Columns("C").Cut
            .Columns("A").Insert
            .Columns("B").Cut
            .Columns("D").Insert
            .Columns("A").Insert
     
    
        ' Step 5 
            .Range("A1").Value = "ID"
            lngLastRow = .Range("B" & .Rows.Count).End(xlUp).Row
            
            .Range("A2:A" & lngLastRow).Formula = _
                "=SUBSTITUTE(" & strFORMULA & ", "".CSV"", """")"
        
 ' This part is incomplete !      
                      
            strFile = Dir$()
        End With
    Loop

End Sub