Yes, but honestly I dont like it.
I installed Filezilla server and everything OK. Then, created a anonymus account without listing permision.
Then with port open, I just put a link like this in the form.
<a href='ftp://123.209.xx.65/F0<<Factura.XFolio>>.PDF'>Descargar PDF</a>
It does work, but again the Invoices has an autonumeric value, so anyone can be able to download documents knowing the files.
Like: Invoice No. F0A100.PDF
If they just know 1 invoice number they can download F0A100.PDF, F0A101.PDF, F0A102.PDF as so on.. Even if that document does not belong to them.
If anyone has a better solution it is welcomed...