Can I still trade if I am F2P?

Yes, as a F2P player, you can trade, but you are limited in what you can.

Drops that you recieve in-game cannot be traded, except for tools (such as crates, keys and name tags). These will have the non-tradeable tag in your inventory.

However, items that other players gift you can be traded. Therefore, if a Premium friend gifts you some items, you can then trade them for something else with someone else.

Should you choose to upgrade, all non-achievement items obtained through drops that are previously non-tradable will be available for trading.
(Achievement items, as always will stay untradable regardless of the account type)