What Am I Riddles

Question: If you throw me out of the window,
I'll leave a grieving wife.
Bring me back, but through a door,
You'll see someone giving life.

What am I?

Question: You are my brother, but I am not your brother. Who am I?

Question: A man shaves several times a day, yet he still has a beard.

Who is this man?

Question: If you have me, you want to share me. If you share me, you haven't got me. What am I?

Question: I have all of your knowledge but could fit in your hands.

What am I?