Maintain CAD references as layers/OCGs in PDF

Product: PDFNet, CADModule

Product Version: Node.js, 9.2.0-1

When converting a DGN which contains references to other DGN’s, I would like the references to be retained as Layers/OCGs in the converted PDF file.

When a DGN contains references to other files, if I export as PDF (using Workstation) the referenced files are available as Layers.

However, if I convert the DGN using PDFTron CADModule, the references are merged into a single layer.

Is it possible to keep references as separate layers in the converted PDF, similar to how the layers are maintained when they are part of the “master” DGN file?