Presenter is the person standing on stage to present his talk. A Non-presenter (co-author)may works with the presenter (Author) on the paper, but the non-presenter do not stand up to give the talk. An observer is someone who did not contribute to the paper at all. But observer aware of the content of the paper, he obsevre what has been going on.

Paper is one or more sheets of paper bearing writing or printing, especially:
a. A formal written composition intended to be published, presented, or read aloud; a scholarly essay or treatise.
b. A piece of written work for school; a report or theme.
c. An official document, especially one establishing the identity of the bearer. Often used in the plural.

Poster is a large, usually printed placard, bill, or announcement, often illustrated, that is posted to advertise or publicize something