What is a pamphlet ?

A pamphlet can be defined to be a small paper-covered book, especially on a question of current interest. Usually, it is written on a controversy regarding political or religious issues stirring the minds of the people. In a pamphlet, arguments are given from the writer's point of view and therefore,  it is not impartial writing. The opinions of the persons who hold different views to the writer's opinion are discussed to be provided false. It can be said to be one-sided failing to represent the universal views. It is not a long treatment of the subject but a brief analysis of what the writer wants to say. As its space is limited,  it cannot deal with the subject in detail. It only focuses on the points that can impress the reader and bring him under his fold. Only a writer of forceful writing can succeed in writing a pamphlet. Since its appeal is temporary,  it does not create any permanent interest in the reader. With time,  it becomes obsolete and passes into oblivion.

Secondly, 

Definition of pamphlet 

A pamphlet is an unbound printed publication with or without a cover. Among the first printed materials pamphlets were widely used in England. It was often written for religious or political propaganda. The subject of the pamphlets was chosen from the controversies that agitated the minds of the contemporary people. In the pamphlets,  the subject matter is not seriously treated and the style is not of notable qualities, because the target was the common people who would not pursue it to the end. Very few pamphlets could leave deep impressions on the age and its readers. Only a few of them could rise to the level of pure literature. Areopagitica is one of the rare pamphlets that are, still regarded with respect.

But the pamphlets written by Milton are not of such qualities. Most of them are written on political controversies but some of them really leave a permanent impression upon the minds of the people. Areopagitica belongs to this group and is considered by most critics to be an immortal piece of literature.