A vendor assessment, particularly a due diligence review, is the most appropriate type of assessment when evaluating a company during an acquisition. This review ensures that the company to be acquired is compliant with necessary security standards and that there are no hidden security liabilities. Penetration testing focuses on finding vulnerabilities in systems and networks and may not cover the broad scope of security measures in place. Self-assessments are internal evaluations and might not provide an objective view needed during an acquisition. Risk analysis is part of the overall risk management process but does not serve as a comprehensive review of a company's security measures during an acquisition scenario.