PixelToNewDpi

public static int PixelToNewDpi(double pixels, double oldDpi, double newDpi)

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);

// Define the size of the top margin of this section in pixels, according to a custom DPI.
const double myDpi = 192;

PageSetup pageSetup = builder.PageSetup;
pageSetup.TopMargin = ConvertUtil.PixelToPoint(100, myDpi);

Assert.AreEqual(37.5d, pageSetup.TopMargin, 0.01d);

// At the default DPI of 96, a pixel is 0.75 points.
Assert.AreEqual(0.75d, ConvertUtil.PixelToPoint(1));

builder.Writeln($"This Text is {pageSetup.TopMargin} points/{ConvertUtil.PointToPixel(pageSetup.TopMargin, myDpi)} " +
                $"pixels (at a DPI of {myDpi}) from the top of the page.");

// Set a new DPI and adjust the top margin value accordingly.
const double newDpi = 300;
pageSetup.TopMargin = ConvertUtil.PixelToNewDpi(pageSetup.TopMargin, myDpi, newDpi);
Assert.AreEqual(59.0d, pageSetup.TopMargin, 0.01d);

builder.Writeln($"At a DPI of {newDpi}, the text is now {pageSetup.TopMargin} points/{ConvertUtil.PointToPixel(pageSetup.TopMargin, myDpi)} " +
                "pixels from the top of the page.");

doc.Save(ArtifactsDir + "UtilityClasses.PointsAndPixelsDpi.docx");