Can I rent a car in Spain and drive it to Portugal? Do I need to go through any procedures ?

Yes, you can just write "transit Portugal" when you place your order. There's no other procedures.

You can just drive through, no problem at all, just the retention time cannot exceed six months.

Please note that when using highways in Portugal, you need to bind a bank card. Be sure to keep the receipt when binding the card, as it will be needed when unbinding. Although you have bound a card, when passing through toll stations, be sure not to use the direct-through lane, but to use the lane for obtaining a pass. Otherwise, it will be very troublesome!

The place for visa should have two, one is below the contract text, and the other is below the fee list. You should pay attention to the details and summary of the fees. They will circle for you to see what you rent, but they will not underline to remind you of the insurance amount.

To communicate with the car rental company.

Can go through, just choose the return location when ordering.