Option Explicit
Sub Test()
Dim DerL&, X&
DerL = Range("A" & Rows.Count).End(xlUp).Row
Range("K1") = "Fichiers"
Range("L1") = "Lien Répertoire"
For X = 2 To DerL
Range("K" & X) = Cells(X, 1) & ".txt"
ActiveSheet.Hyperlinks.Add Anchor:=Cells(X, 12), Address:= _
"C:\Users\Jean-Claude\Downloads\Lien" & Cells(X, 1) & ".txt", TextToDisplay:="Lien " & Cells(X, 1) & ".txt"
Next X
End Sub