Paperback
Can you trash cards from your hand whenever you want, and can you trash a card you used to build your word?
The rulebook's Hand definition means the unused cards, and trashing needs a card that allows it.
No. Cards are trashed only when a card you played in the word allows it, and only cards left in hand can be trashed. Cards used to build the word cannot be trashed from hand. Where a card says 'may', the trash is optional.