Answer:
I am a person who pretends to be someone else
I am always around you but often forgotten. I am pure and clean most of the time, but occasionally rotten. What am I?
I am needed for most animals and hardcover books. What am I?
Die without me, never thank me. Walk right through me, never feel me. 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?
When someone uses this acronym, you know you've got to pick up the pace