[ecfisa]

Hola gdlrinfo.

Código Delphi [-]
procedure ChangeExt(Folder: string; const NewExt: string);
var
  sr: TSearchRec;
begin
  Folder:= IncludeTrailingPathDelimiter(Folder);
  if FindFirst(Folder+'*.*', faAnyFile, sr) = 0 then
  begin
    repeat
      if (sr.Name <> '.')and(sr.Name <> '..') and
         (sr.Attr and faDirectory <> faDirectory) then
      begin
        RenameFile(Folder + sr.Name,
          Folder + ChangeFileExt(ExtractFileName(sr.Name), '') + '.' + NewExt);
      end;
    until FindNext(sr) <> 0;
    FindClose(sr);
  end;
end;

Ejemplo de uso:

Código Delphi [-]
procedure TForm1.Button1Click(Sender: TObject);
begin
  ChangeExt('C:\CARPETA', 'DOC');
end;

Saludos