DPart can be added to a PDF file using Quick Fix as described in a chapter of the QuickFix feature overview.

The InjectDPart feature in Quick Fix uses a page list as input. In a Process Plan this list can be dynamically created. pdfToolbox (version 12 or newer) has a predefined Process Plan "Create DPart record information from headings" that does so. It uses the text size as an indication for a heading and creates a DPart structure in which each page with a heading is referenced as a record start.