How to: Use PDF Facade API to Clear Page Content

Oct 19, 2021
3 minutes to read

The following article describes how to use PDF Facade API to clear PDF page content.

Important

The Universal Subscription or an additional Office File API Subscription is required to use this example in production code. Refer to the DevExpress Subscription page for pricing information.

The PdfViewerExtensions.GetDocumentFacade method retrieves a PdfDocumentFacade class object that allows you to change the PDF document without access to its inner structure.

The PdfDocumentFacade.Pages property returns a list of PdfPageFacade objects that contain PDF page properties. Call the ClearContent method to remove content in one or multiple page areas. You can specify what content type to keep in the areas that are to be cleared. To do that, pass the PdfClearContentOptions class object as the method parameter.

The code sample below removes only text in selected page area:

C#
VB.NET

csharp

using DevExpress.Pdf;
using System;
using System.Windows.Input;

PdfDocumentPosition startSelectionPosition;

public MainWindow()
{
    InitializeComponent();
    pdfViewer.OpenDocument("Demo.pdf");
    pdfViewer.MouseDown += PdfViewer_MouseDown;
    pdfViewer.MouseUp += PdfViewer_MouseUp;
}

private void PdfViewer_MouseUp(object sender, MouseButtonEventArgs e)
{
    // Retrieve the end position of the selection
    PdfDocumentPosition endSelectionPosition =
         pdfViewer.ConvertPixelToDocumentPosition(e.GetPosition(pdfViewer));
    if (endSelectionPosition == null || startSelectionPosition == null) return;
    if (endSelectionPosition.Point.Equals(startSelectionPosition.Point)) return;

    // Define the selection area
    double left = Math.Min(startSelectionPosition.Point.X, endSelectionPosition.Point.X);
    double bottom = Math.Min(startSelectionPosition.Point.Y, endSelectionPosition.Point.Y);
    double right = Math.Max(startSelectionPosition.Point.X, endSelectionPosition.Point.X);
    double top = Math.Max(startSelectionPosition.Point.Y, endSelectionPosition.Point.Y);
    PdfRectangle rectangle = new PdfRectangle(left, bottom, right, top);
    int pageNumber = startSelectionPosition.PageNumber;

    // Retrieve the page properties
    PdfPageFacade pageFacade = pdfViewer.GetDocumentFacade().Pages[pageNumber - 1];

    // Set what content type to keep
    PdfClearContentOptions options = new PdfClearContentOptions()
    {
        ClearAnnotations = false,
        ClearGraphics = false,
        ClearImages = false
    };

    // Clear the selected area
    pageFacade.ClearContent(rectangle, options);
}

private void PdfViewer_MouseDown(object sender, MouseButtonEventArgs e)
{
    // Get the start position of the selection
    startSelectionPosition = pdfViewer.ConvertPixelToDocumentPosition(e.GetPosition(pdfViewer), true);
    if (startSelectionPosition == null) return;
}

Imports DevExpress.Pdf
Imports System
Imports System.Windows.Input

Private startSelectionPosition As PdfDocumentPosition

Public Sub New()
    InitializeComponent()
    pdfViewer.OpenDocument("Demo.pdf")
    AddHandler pdfViewer.MouseDown, AddressOf PdfViewer_MouseDown
    AddHandler pdfViewer.MouseUp, AddressOf PdfViewer_MouseUp
End Sub

Private Sub PdfViewer_MouseUp(ByVal sender As Object, ByVal e As MouseButtonEventArgs)
    ' Retrieve the end position of the selection
    Dim endSelectionPosition As PdfDocumentPosition =
         pdfViewer.ConvertPixelToDocumentPosition(e.GetPosition(pdfViewer))
    If endSelectionPosition Is Nothing OrElse startSelectionPosition Is Nothing Then
        Return
    End If
    If endSelectionPosition.Point.Equals(startSelectionPosition.Point) Then
        Return
    End If

    ' Define the selection area
    Dim left As Double = Math.Min(startSelectionPosition.Point.X, endSelectionPosition.Point.X)
    Dim bottom As Double = Math.Min(startSelectionPosition.Point.Y, endSelectionPosition.Point.Y)
    Dim right As Double = Math.Max(startSelectionPosition.Point.X, endSelectionPosition.Point.X)
    Dim top As Double = Math.Max(startSelectionPosition.Point.Y, endSelectionPosition.Point.Y)
    Dim rectangle As New PdfRectangle(left, bottom, right, top)
    Dim pageNumber As Integer = startSelectionPosition.PageNumber

    ' Retrieve the page properties
    Dim pageFacade As PdfPageFacade = pdfViewer.GetDocumentFacade().Pages(pageNumber - 1)

    ' Set what content type to keep
    Dim options As New PdfClearContentOptions() With {.ClearAnnotations = False, .ClearGraphics = False, .ClearImages = False}

    ' Clear the selected area
    pageFacade.ClearContent(rectangle, options)
End Sub

Private Sub PdfViewer_MouseDown(ByVal sender As Object, ByVal e As MouseButtonEventArgs)
    ' Get the start position of the selection
    startSelectionPosition = pdfViewer.ConvertPixelToDocumentPosition(e.GetPosition(pdfViewer), True)
    If startSelectionPosition Is Nothing Then
        Return
    End If
End Sub