stuck when save file as pdf in folder has created

Hello

I'm stuck  when  try  save  file  as  pdf to  current  month but  it  gives error 

can't  save  document  or  document  is open  in this  line 

Rng.ExportAsFixedFormat Type:=xlTypePDF, Filename:=PDFfile, _
            Quality:=xlQualityStandard, IncludeDocProperties:=True, IgnorePrintAreas:=False, OpenAfterPublish:=False

Sub ExportSheetToPDF()
'
    Const openPDFwhenDone = True

    'Set constant basePath to the file save path
    Const basePath = "C:\Users\PC WORLD\Desktop\TextFolder\"

    'Declare variable pdfPath which for the complete path & filename
    Dim pdfPath As String
    Dim lr As Long
   Dim WS As Worksheet
   Set WS = Sheets("ST")


     lr = WS.Cells(Rows.Count, 1).End(xlUp).Row
     Set Rng = WS.Range("a1:F" & lr)

    'get the name of the "year" folder
    pdfPath = basePath & Year(Date)

    'if the "year" folder doesn't exist then create it
    If Dir(pdfPath, vbDirectory) = "" Then MkDir pdfPath

    'get the name of the "month" folder
    pdfPath = pdfPath & "\" & Format(Month(Date), "00")

    'if the "month" folder doesn't exist then create it
    If Dir(pdfPath, vbDirectory) = "" Then MkDir pdfPath

    'get the complete pdf filename
   If Right(PDFfile, 1) <> "\" Then PDFfile = PDFfile & "\"
   PDFfile = PDFfile & WS.Range("F6")


    'export active worksheet as PDF to pdfPath
    Rng.ExportAsFixedFormat Type:=xlTypePDF, Filename:=PDFfile, _
            Quality:=xlQualityStandard, IncludeDocProperties:=True, IgnorePrintAreas:=False, OpenAfterPublish:=False
    'make sure the pdf file was created
    If Dir(pdfPath) = "" Then
        'file not found
        MsgBox "Something went wrong. (PDF wasn't created.)"
    Else
        'Success!  Show success message (unless PDF was set to auto-open)
        If Not openPDFwhenDone Then MsgBox "File Saved As:" & vbLf & pdfPath
    End If

End Sub

the  code  should  save  in  folder 06  within folder 2023    and  the  name  file  is  based on cell F6 and  should save  the  range  A1: F,  not  the  whole  sheet

thanks