Written with people moving from Turkey in mind. The Portuguese rules still apply more broadly.
14-Day Return Right (Online)
For any product bought online (distance selling), you have a legal "Cooling Off Period" of 14 days to return it for a full refund without giving any reason. This applies even if the package has been opened (but the item must be undamaged).
The seller must reimburse you within 14 days of receiving the return request. This protection does not apply to in-store purchases, where returns are a courtesy, not a legal right (unless defective).