A right-wing extremist vigillante, Rorshach, discovers that a murdered man is The Comedian, another costumed adventurer. This triggers an investigation that causes him to track down and interview his former team members, the Watchmen. In a world that has been drastically changed by the superhuman powers of one of those members, Dr. Manhattan, the team members start to reconsider who they are on the midst of a complex situation that seems to push events even closer to the brink of an impending global disaster.
Watchmen used false documents in a centrally important way, especially because verisimiltude in general was so important as it worked in opposition to the cartoonish origins of the material. So, while the work is not entirely composed of false documents, the documents that are used have a central thematic and technical role in the drama... especially Rorshach's psychiatric history and the Pirate Comic that plays as counterpoint to the larger narrative (and is the product of one of the kidnapped artists).
The whole book, in a way, is about levels of authenticity. Is Roshsach the real masked hero because of his intense personal conviction, or is it Night Owl because of the level of energy and money that he dedicated to more and more elaborate toys and masks?
The book is all about props and masks and a general investigation of "realness" and "perfection." It tries to inspect the depth and literality of an Ubermensch in a naturlistic setting. There is a kind of arms race of realness going on in the evolution of super heros as described by the book, starting with a masked wrestler, then a masked cop, then techno-dilletantes and madmen and vigalantes, finally culminating in Doctor Manhattan--the hero that is so "real" that he not only makes superheroes obsolete, he makes all of mankind irrelevant.