Answer:
I am in the past never in the future. I don't exist but have existed. I saw what you saw and that is what I will ever see.
I'm white and used for cutting and grinding. When I'm damaged, humans usually remove or fill me. For most animals I am a useful tool. What am I?
People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?
While you were folding a letter you got me. Usually you will do whatever it takes to avoid me but now you can't help but find me.
I am your most powerful weapon; I come before your eyes. I help you seek the truth, yet I often give you lies. What am I?
A little house full of meat, no door to go in and eat.