How to add and remove the layers to and from an existing PDF Document?

Add Layers:
//Loads the Pdf document
PdfLoadedDocument doc = new PdfLoadedDocument("file.pdf");
//Gets the particular page from loaded pages.
PdfLoadedPage page = doc.Pages[0] as PdfLoadedPage;
//Gets the Layers of particular loaded page
PdfPageLayerCollection coll = doc.Pages[0].Layers;
 //Add the first layer
PdfPageLayer layer = page.Layers.Add("Layer1");
layer.PrintState = PdfPrintState.NeverPrint;
//Layer1 graphics
PdfGraphics graphics = layer.Graphics;
//Applying translation
graphics.TranslateTransform(100, 60);
//Draw Arc 
PdfPen pen = new PdfPen(System.Drawing.Color.Red, 50);
RectangleF rect = new RectangleF(0, 0, 50, 50);
graphics.DrawArc(pen, rect, 360, 360);
pen = new PdfPen(System.Drawing.Color.Blue, 30);
graphics.DrawArc(pen, 0, 0, 50, 50, 360, 360);
//Add another layer on the page
PdfPageLayer layer2 = page.Layers.Add("Layer2");
//Layers 2 graphics
graphics = layer2.Graphics;
graphics.TranslateTransform(100, 180);
graphics.SkewTransform(0, 50);
//Draw another set of elements
pen = new PdfPen(System.Drawing.Color.Red, 50);
graphics.DrawArc(pen, rect, 360, 360);
pen = new PdfPen(System.Drawing.Color.Blue, 30);
graphics.DrawArc(pen, 0, 0, 50, 50, 360, 360);
//Add another layer
PdfPageLayer layer3 = page.Layers.Add("Layer3");
// Layer 3 graphics
graphics = layer3.Graphics;
graphics.TranslateTransform(160, 120);
 //Draw another set of elements.
pen = new PdfPen(System.Drawing.Color.Red, 50);
graphics.DrawArc(pen, rect, -60, 60);
pen = new PdfPen(System.Drawing.Color.Blue, 30);
graphics.DrawArc(pen, 0, 0, 50, 50, -60, 60);
pen = new PdfPen(System.Drawing.Color.Yellow, 20);
 //Save to disk
doc.Save("Sample.pdf");
doc.Close();
Remove Layers:
PdfLoadedDocument doc = new PdfLoadedDocument("sample.pdf");
//Gets the layers of particular loaded page
PdfPageLayerCollection coll = doc.Pages[0].Layers;
//Removes the layer using Name
 coll.Remove("Layer1");