public void ClearContent(
    PdfOrientedRectangle rect,
    bool usePageCoordinateSystem
)

Public Sub ClearContent(
    rect As PdfOrientedRectangle,
    usePageCoordinateSystem As Boolean
)

using (PdfDocumentProcessor pdfDocumentProcessor = new PdfDocumentProcessor())
{
    // Load a document
    pdfDocumentProcessor.LoadDocument("Document.pdf");

    // Define the upper half of the first page
    PdfRectangle cropBox = pdfDocumentProcessor.Document.Pages[0].CropBox;
    PdfOrientedRectangle pageRectangle =
      new PdfOrientedRectangle(cropBox.TopLeft, cropBox.Width, cropBox.Height / 2, 0);

    // Obtain the first page properties
    PdfPageFacade pageFacade = pdfDocumentProcessor.DocumentFacade.Pages[0];

    // Clear the upper half of the page
    pageFacade.ClearContent(pageRectangle, true);

    // Save the result
    pdfDocumentProcessor.SaveDocument("Document_cleared.pdf");
}

Using pdfDocumentProcessor As New PdfDocumentProcessor()
  ' Load a document
  pdfDocumentProcessor.LoadDocument("Document.pdf")

  ' Define the upper half of the first page
  Dim cropBox As PdfRectangle = pdfDocumentProcessor.Document.Pages(0).CropBox
  Dim pageRectangle As
     New PdfOrientedRectangle(cropBox.TopLeft, cropBox.Width, cropBox.Height \ 2, 0)

  ' Obtain the first page properties
  Dim pageFacade As PdfPageFacade = pdfDocumentProcessor.DocumentFacade.Pages(0)

  ' Clear the upper half of the page
  pageFacade.ClearContent(pageRectangle, True)

  ' Save the result
  pdfDocumentProcessor.SaveDocument("Document_cleared.pdf")
End Using