ZoomFactor

public int ZoomFactor { get; set; }

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);
builder.Writeln("Hello world!");

// Create a "PdfSaveOptions" object that we can pass to the document's "Save" method
// to modify how that method converts the document to .PDF.
// Set the "ZoomBehavior" property to "PdfZoomBehavior.ZoomFactor" to get a PDF reader to
// apply a percentage-based zoom factor when we open the document with it.
// Set the "ZoomFactor" property to "25" to give the zoom factor a value of 25%.
PdfSaveOptions options = new PdfSaveOptions
{
    ZoomBehavior = PdfZoomBehavior.ZoomFactor,
    ZoomFactor = 25
};

// When we open this document using a reader such as Adobe Acrobat, we will see the document scaled at 1/4 of its actual size.
doc.Save(ArtifactsDir + "PdfSaveOptions.ZoomBehaviour.pdf", options);