Which document formally advises a defendant of a legal complaint?

The correct choice is the summons, which serves as a formal notification to a defendant that a legal complaint has been filed against them. It is a crucial component of civil procedure, as it notifies the defendant that they are being sued, provides details about the complaint, and outlines the time frame within which they need to respond.

The summons is designed to ensure that the defendant is aware of the proceedings and has the opportunity to present a defense or respond to the claims made against them. This process is an essential part of upholding the principles of due process, allowing defendants the chance to participate in the legal process and defend their rights.

In contrast, the other options serve different purposes in the civil process. A writ of possession relates to the enforcement of an eviction or the recovery of property, while a notice of trial provides information about the scheduling of a trial rather than alerting a defendant to a complaint. An order of execution pertains to the enforcement of a judgment after a court has ruled in a case. Each of these documents plays a specific role in the legal system, but only a summons directly notifies the defendant of the existence of a legal complaint.