如何使用c#从itext7列表中删除项目？

Document document = new Document();

PdfReader reader = new PdfReader("existing_document.pdf");

PdfWriter writer = new PdfWriter("new_document.pdf");

PdfDocument existingDocument = new PdfDocument(reader);
PdfDocument newDocument = new PdfDocument(writer);
existingDocument.CopyPagesTo(1, existingDocument.GetNumberOfPages(), newDocument);

PdfPage page = newDocument.GetFirstPage();
PdfCanvas canvas = new PdfCanvas(page);
PdfTextExtractor extractor = new PdfTextExtractor(page);
IList<ITextChunk> chunks = extractor.GetResultantTextChunks();

foreach (ITextChunk chunk in chunks)
{
    if (chunk.GetText().Contains("要删除的项目"))
    {
        canvas.Rectangle(chunk.GetBoundingRectangle());
        canvas.SetFillColor(ColorConstants.White);
        canvas.Fill();
    }
}

existingDocument.Close();
newDocument.Close();