How to Insert workbook name in all worksheets in first column of all rows (used rows) in a folder

Question

I have a task to add workbook name into all worksheet's first column hence i need to have a macro and below is a draft of the same

Sub InsertWorkbookName()
Path = "C:\Users\mechee69\Download\"
Filename = Dir(Path & "*.xls")

Do While Filename <> ""
Workbooks.Open Filename:=Path & Filename, ReadOnly:=True
For Each Sheet In ActiveWorkbook.Sheets
Columns("A:A").Select
Selection.Insert Shift:=xlToRight, CopyOrigin:=xlFormatFromLeftOrAbove
Range("A1").Select
ActiveCell.SpecialCells(xlLastCell).Select
Application.Goto Range("A" & ActiveCell.Row), True
ActiveCell.Select
ActiveCell.FormulaR1C1 = _
    "=RIGHT(LEFT(CELL(""filename""),FIND(""."",CELL(""filename""),FIND(""["",CELL(""filename""),1))-1),FIND(""."",CELL(""filename""),FIND(""["",CELL(""filename""),1))-FIND(""["",CELL(""filename""),1)-1)"
Application.Goto Range("A" & ActiveCell.Row), True
ActiveCell.Select
Selection.Copy
Range(Selection, Selection.End(xlUp)).Select
ActiveSheet.Paste
Application.CutCopyMode = False
Selection.Copy
Selection.PasteSpecial Paste:=xlPasteValues, Operation:=xlNone, SkipBlanks _
    :=False, Transpose:=False
Application.CutCopyMode = False
ActiveWorkbook.Save
Next Sheet
Workbooks(Filename).Close
Filename = Dir()
Loop
End Sub

Answer 1

So this Macro will open Excel Files in a Folder with a specific format, then it prints the workbookname in A1 in every sheet of that file. It ignores the master, if its in the same folder.

Sub WorkbookName()
Dim wbk As Workbook
Dim Filename As String
Dim Path As String
Dim lastRow As Long
Dim lSecurity As Long

On Error Resume Next

Path = "C:\Users\User\Desktop\Files\" 'Folder of your Files
Filename = Dir(Path & "*.xlsx") 'Format of your files

Do While Filename <> "" And Filename <> "Master.xlsm" 'Dont Open MasterFile
    Set wbk = Workbooks.Open(Path & Filename)
    lSecurity = Application.AutomationSecurity
    Application.AutomationSecurity = msoAutomationSecurityLow

    For Each ws In wbk.Worksheets
        With ws
            .Range("A1").EntireColumn.Insert
            lastRow = .Cells(Rows.Count, 2).End(xlUp).Row
            .Range(Cells(1, 1), Cells(lastRow, 1)).Value = ActiveWorkbook.Name

        End With
    Application.AutomationSecurity = lSecurity
    Next ws
wbk.Close True
Filename = Dir
Loop
End Sub