What Am I Riddles

Question: What is only a small box but can weigh over a hundred pounds?

Question: When you bend me I'm kind
But I'm very hard to find
I'm easily sold
and rhyme with this when told

What am I?

Question: I have roots that nobody sees,
I'm taller than any trees,
up and up I go,
but I never grow?

What am I?

Question: If a man carried my burden, he'd break his back.
I am not rich, but I always leave silver in my track.

What am I?

Question: While you were folding a letter I got you.
Usually you will do whatever it takes to avoid me,
but now you can't help but find me.

What am I?