No, papers is not a collective noun. 'Papers' refer to more than one sheet of paper Just like 'dogs' means many dogs. Collective noun is a type of noun that is use to group people, animals, place or items. It is usually in singular forms but collective nouns can also be in plural forms. Examples - Board of Directors, which means a group of directors. Herds of cattle means many groups of cattle that are together.
The right words for a collection of paper will be 'sheets of paper or pad of paper'. This refers to all the papers put together in one place. Papers is not a collective noun.
The word 'papers' refers to multiple pieces of paper. If the writer or person speaking about multiple sheets of paper needs a collective term for paper, he should explore the use of the words 'ream,' 'stack,' or 'pad.' Collective nouns refer to a group of things.
The word 'team,' for instance, would include all the players of a baseball or basketball team. A ream, pad, or stack would include all of the paper together in that one grouping.