Code

void TestPdf()
{
	diagram.ClearAll();

	var inch = (float)MeasureUnit.Inch.Convert(1, MeasureUnit.Millimeter, null);
	diagram.Bounds = new RectangleF(0, 0, 400 * inch, 400 * inch);

	for (int i = 0; i < 400; i++)
	{
		var node = diagram.Factory.CreateShapeNode(
			i * inch, i * inch, 0.9f * inch, 0.9f * inch);
		node.Text = i.ToString();
	}

	var exporter = new PdfExporter();
	exporter.PageSize = PageSize.A4;
	exporter.Export(diagram, "test1.pdf");

	diagram.Bounds = new RectangleF(0, 0, 199 * inch, 199 * inch);
	exporter.Scale = 50.0f;
	exporter.PageSize = PageSize.DiagramSize;
	exporter.Export(diagram, "test2.pdf");
} 

Code

void TestPdf()
{
	//int sizeTest = 800;
	//int sizeTest = 400;
	int sizeTest = 250;

	diagram.ClearAll();

	var inch = (float)MeasureUnit.Inch.Convert(1, MeasureUnit.Millimeter, null);
	diagram.Bounds = new RectangleF(
		0, 0, sizeTest * inch, sizeTest * inch);

	for (int i = 0; i < sizeTest; i++)
	{
		var node = diagram.Factory.CreateShapeNode(
			i * inch, i * inch, 0.9f * inch, 0.9f * inch);
		node.Text = i.ToString();
	}

	var exporter = new PdfExporter();

	// margin size in inches
	var m = exporter.Margins;
	var mw = (m.Left + m.Right) / 100;
	var mh = (m.Top + m.Bottom) / 100;

	// max size supported by PDF Reader
	var scaleTo = diagram.Bounds;
	scaleTo.Width = (200 - mw) * inch;
	scaleTo.Height = (200 - mh) * inch;

	// set Bounds to max size
	var diagBounds = diagram.Bounds;
	diagram.Bounds = scaleTo;

	// scale to fit original bounds into max size
	exporter.Scale = 100 * Math.Min(
		scaleTo.Width / diagBounds.Width,
		scaleTo.Height / diagBounds.Height);

	// export
	exporter.PageSize = PageSize.DiagramSize;
	exporter.Export(diagram, "test2.pdf");

	// restore original Bounds
	diagram.Bounds = diagBounds;
}