Describe the existence, structure and scope of the proprietary material and the applicant's role in relation to it, rather than reproducing the material itself. Internal document control records, training logs and revision histories carry the point without disclosing content.
Prove the shape, not the contents
A reviewer needs to be satisfied that something company-specific exists and that this person knows it. That can be shown with a controlled-document index listing internal procedures by number, title and revision date, with the technician recorded as author or approver on several of them. It can be shown with training records tying the person to internal courses that outsiders cannot take. It can be shown with a service history listing commissioned units and escalations. None of that requires disclosing the brine chemistry or the control logic. Where a document must be summarised, have someone who understands both the system and the petition write the summary, and state who wrote it and on what basis. If any underlying record is not in English, remember that a full certified translation is ordinarily required rather than a summary.
Hypothetical example: A medical-device calibration specialist has access to a restricted internal procedure library, yet the employer's first draft relies only on a résumé. The first review should identify the records that connect the person to the restricted material: training completion logs, access records, version-controlled procedures, supervisor declarations, and project artifacts. Each document should explain a fact, not merely repeat the conclusion. Payroll documents establish dates, while technical exhibits establish the knowledge. Redact genuinely confidential detail carefully but retain enough substance to show why it is company-specific. A public patent alone may prove ownership, not that the transferee possesses advanced internal know-how.