Matterhorn Protocol

A comprehensive set of test conditions published by the PDF Association for verifying PDF/UA (ISO 14289-1) conformance. The Matterhorn Protocol categorizes accessibility checks into those that can be performed by automated tools and those that require human judgment, providing a structured framework for systematic PDF accessibility evaluation. It identifies 31 checkpoints with 136 individual failure conditions covering document structure, metadata, fonts, colour contrast, alternative text, and interactive elements. The protocol is widely used by PDF accessibility checkers and auditors as a reference standard, and its distinction between machine-checkable and human-checkable criteria acknowledges the fundamental limitation that automated tools alone cannot fully verify accessibility.