You may trash this card.
If you do, choose one:
+1 Card; +1 Action; +1 Buy; + 1 Coin.
You always get the +1 Card and +1 Action when you put this card into play, and can look at the card you draw before you have to make the decision to trash this or not. However you have to make the decision before moving on to other Actions or other Phases. You cannot retroactively trash this later in your turn. If you decide to trash it, it is removed from play, and you must make the choice immediately which effect you would like to have happen.
Although the Encampment card is trashed, it still counts as you having played an Action for the purposes of cards like the Peddler.
Copying this card via Throne Room or King's Court will not allow you to trash it multiple times, although you will still get the +1 Action and +1 Card for each copy.