// Create named layers
var base_ = doc.CreateOptionalContentGroup(
    "Base Drawing", visible: true);
var dims = doc.CreateOptionalContentGroup(
    "Dimensions", visible: true);
var notes = doc.CreateOptionalContentGroup(
    "Notes", visible: false);

// Base layer content
page.BeginOptionalContent(base_);
page.FillRectangle(100, 400, 200, 150,
    new PdfDrawOptions {
        FillColor = new PdfColor(0.9, 0.9, 0.95)
    });
page.EndOptionalContent();

// Dimensions overlay
page.BeginOptionalContent(dims);
page.AddText("200 pt", 160, 560,
    new PdfTextOptions {
        FontSize = 9,
        Color = new PdfColor(0.8, 0, 0)
    });
page.EndOptionalContent();

// Hidden notes layer
page.BeginOptionalContent(notes);
page.AddText("NOTE: dimensions in points",
    100, 380);
page.EndOptionalContent();