According to IIA guidance, due professional care means that internal auditors must apply the care and skill expected of a reasonably prudent and competent internal auditor. This involves considering the cost of assurance in relation to potential benefits and exercising judgment and care in accordance with the complexity of the task. It does not imply an exhaustive review of all transactions or guarantees that all significant risks will be identified or that fraud does not exist.
The Institute of Internal Auditors (IIA) - International Standards for the Professional Practice of Internal Auditing, specifically those related to due professional care.

The requirements for proficiency, according to the IIA guidance, include sufficient consideration of current activities, trends, and emerging issues (1), providing relevant advice and recommendations to management and the board (2), and possessing the necessary knowledge, skills, and other competencies for their responsibilities during engagements (4). These elements ensure that internal auditors are well-prepared and effective in their roles.
IIA's International Standards for the Professional Practice of Internal Auditing

According to the Standards, internal audit professional development plans must ensure that staff development activities are based primarily on the skills and competencies needed to complete the audit plan. This requirement ensures that the internal audit staff possesses the necessary expertise and capabilities to effectively carry out the planned audit activities.
IIA Standards related to Continuing Professional Development and Staff Proficiency.

Loss of intellectual property is a significant strategic risk that internal auditors should consider when performing a third-party risk management engagement. This risk can have substantial implications for the organization's competitive advantage, reputation, and financial performance. Ensuring that third parties have adequate controls to protect intellectual property is essential for mitigating this risk. Internal auditors should evaluate the effectiveness of these controls and the potential impact of intellectual property loss on the organization's strategic objectives.
The IIA Standards: Standard 2120 - Risk Management: "The internal audit activity must evaluate the effectiveness and contribute to the improvement of risk management processes." IIA Practice Guide: "Auditing Third-party Risk Management": Highlights the importance of assessing strategic risks, including intellectual property protection, in third-party relationships.

The source of authority for an engagement supervisor to make contact with external parties, such as obtaining maintenance reports from a contractor, typically comes from the provisions outlined in the internal audit charter. This charter formally defines the purpose, authority, and responsibility of the internal audit activity, including interactions with third-party service providers. It is essential as it sets the audit activity's scope, allowing auditors to access necessary information and resources.
The Institute of Internal Auditors (IIA) - International Professional Practices Framework (IPPF), specifically the Audit Charter guidelines.