iText 7 - Add and Remove Watermark on a PDF

I would like to add and remove a watermark to a PDF using iText 7. I was able to add the watermark, but unable to remove it again. I could only find relevant code/examples related to iText 5. Any pointers appreciated, thanks.

This is how I added the Watermark (using Layers):

            pdfDoc = new PdfDocument(new PdfReader(sourceFile), new PdfWriter(destinationPath));
            var numberOfPages = pdfDoc.GetNumberOfPages();

            PageSize ps = pdfDoc.GetDefaultPageSize();

            for (var i = 1; i <= numberOfPages; i++)
            {
                PdfPage page = pdfDoc.GetPage(i);
                PdfLayer layer = new PdfLayer("watermark", pdfDoc);
                var canvas = new PdfCanvas(page);
                var pageSize = page.GetPageSize();
                var paragraph = new Paragraph(message.WatermarkText).SetFontSize(60);
                paragraph.SetFontColor(Color.BLACK, 0.2f);

                Canvas canvasModel;
                canvas.BeginLayer(layer);
                canvasModel = new Canvas(canvas, pdfDoc, ps);
                canvasModel.ShowTextAligned(paragraph, pageSize.GetWidth() / 2, pageSize.GetHeight() / 2, pdfDoc.GetPageNumber(page), TextAlignment.CENTER, VerticalAlignment.MIDDLE, 45);
                canvasModel.SetFontColor(Color.GREEN, 0.2f);
                canvas.EndLayer();
            }
            pdfDoc.Close();

This is what I have tried to remove the watermark. I want to remove it completely, not just set the layer to not display.(any sample code appreciated):

            pdfDoc = new PdfDocument(new PdfReader(sourceFile), new PdfWriter(destinationPath));                     
             IList<PdfLayer> layers = pdfDoc.GetCatalog().GetOCProperties(true).GetLayers();              

            for (var i = 0; i <= layers.Count; i++)
            {
                var t = layers[i].GetPdfObject().Get(PdfName.Name);

                if (t.ToString().Equals("watermark"))
                {
                        //Not what I want..need to remove the layer
                        layers[i].SetOn(false);
                        //This does not work...
                        //layers.RemoveAt(i);
                    }
                }
                pdfDoc.Close();