To meet the technical requirements for identifying and protecting confidential documents (specifically those following a specific pattern like "Confidential" followed by a seven-digit number), you must first define what the system should look for. A Sensitive Information Type (SIT) is the foundational component in Microsoft Purview for identifying specific data patterns.

Since the requirement involves a specific string ("Confidential") followed by a fixed-length numeric pattern (seven digits), a Regular Expression (Regex) is the most precise and appropriate detection method. Other methods like dictionaries or keywords are less effective for variable numeric strings, and file type detection does not inspect content patterns. Once the SIT is created, it can then be used within sensitivity labels or DLP policies.

Microsoft Purview Documentation: "Custom sensitive information types" section. Details the workflow of creating a SIT before applying it to policies. [Document ID: sensitive-information-type-learn-about]

Microsoft Purview Documentation: "Create custom sensitive information types in the compliance portal." Specifically covers the use of Primary patterns and Regular expressions (Regex) for pattern matching. [Section: "Part 2: Add a pattern"]

Microsoft Purview Documentation: "Regulatory compliance and data classification." Explains that SITs are the building blocks for labeling and data loss prevention strategies. [Section: "Data Classification"]