Hi,
PdfDocument.SaveToFile in current version 10.2.0 loses the OCG layers of the PDF.
The content is still there, but the layers themselves are not saved, even when newly created with doc.Layers.AddLayer and layer.CreateGraphics(page.Canvas).
This was working in versions 8.6.0 and 8.7.2 (which I reverted to now).
Hope you can patch this regression soon,
K.