A "watermark" is a text or an image that appears in front of existing document content.
For example, you could apply a "Confidential" watermark to PDF pages with sensitive information.
"PDF Reader+Writer" edition of
VintaSoft PDF .NET Plug-in provides functionality for adding watermarks to pages of PDF document.
In order to don't overlap the text of PDF document the watermark should be added in "Multiply" color blending mode.
One watermark resource is used for all pages of document to create a PDF with optimal size.
A raster image or vector PDF document can be defined as watermark.
Here is C# code, which allows to add a watermark into PDF document:
// The project, which uses this code, must have references to the following assemblies:
// - Vintasoft.Imaging
// - Vintasoft.Imaging.Pdf
/// <summary>
/// Adds the watermark image to the PDF document.
/// </summary>
/// <param name="inPdfFilename">The filename of input PDF document.</param>
/// <param name="outPdfFilename">The filename of output PDF document.</param>
/// <param name="watermarkImageFilename">The filename of watermark image.</param>
public static void AddWatermarkToPdfDocument(string inPdfFilename, string outPdfFilename, string watermarkImageFilename)
{
AddWatermarkToPdfDocument(inPdfFilename, outPdfFilename, watermarkImageFilename, 0.25f, new Vintasoft.Imaging.PaddingF(0.1f), false);
}
/// <summary>
/// Adds the watermark image to the PDF document.
/// </summary>
/// <param name="inPdfFilename">The filename of input PDF document.</param>
/// <param name="outPdfFilename">The filename of output PDF document.</param>
/// <param name="watermarkImageFilename">The filename of watermark image.</param>
/// <param name="watermarkImageAlpha">The watermark image alpha.</param>
/// <param name="watermarkImagePadding">The watermark image padding.</param>
/// <param name="ignorePageRotation">Indicates that value of Vintasoft.Imaging.Pdf.Tree.PdfPage.Rotate property should be ignored.</param>
public static void AddWatermarkToPdfDocument(
string inPdfFilename,
string outPdfFilename,
string watermarkImageFilename,
float watermarkImageAlpha,
Vintasoft.Imaging.PaddingF watermarkImagePadding,
bool ignorePageRotation)
{
// check watermark padding
if (watermarkImagePadding.Horizontal < 0 || watermarkImagePadding.Vertical < 0)
throw new System.ArgumentOutOfRangeException("watermarkImagePadding");
// open PDF document
using (Vintasoft.Imaging.Pdf.PdfDocument document = new Vintasoft.Imaging.Pdf.PdfDocument(inPdfFilename))
{
// create "watermark" resource
Vintasoft.Imaging.Pdf.Tree.PdfResource watermakResource;
using (Vintasoft.Imaging.VintasoftImage watermarkImage = new Vintasoft.Imaging.VintasoftImage(watermarkImageFilename))
{
// if watermarkImage is PDF page
if (watermarkImage.SourceInfo.DecoderName == "Pdf")
{
// create form resource based on PDF page
Vintasoft.Imaging.Pdf.Tree.PdfPage page = Vintasoft.Imaging.Pdf.PdfDocumentController.GetPageAssociatedWithImage(watermarkImage);
watermakResource = new Vintasoft.Imaging.Pdf.Tree.PdfFormXObjectResource(document, page);
}
else
{
// create watermark image resource with JPEG compression
Vintasoft.Imaging.Pdf.PdfCompression watermarkResourceCompression = Vintasoft.Imaging.Pdf.PdfCompression.Jpeg;
watermakResource = new Vintasoft.Imaging.Pdf.Tree.PdfImageResource(document, watermarkImage, watermarkResourceCompression);
}
}
// for each page in PDF document
foreach (Vintasoft.Imaging.Pdf.Tree.PdfPage page in document.Pages)
{
// add watermark on PDF page
AddWatermarkToPdfPage(page, watermakResource, watermarkImagePadding, watermarkImageAlpha, ignorePageRotation);
}
// pack PDF document to an output file
document.Pack(outPdfFilename);
}
}
/// <summary>
/// Adds the watermark image to the PDF page.
/// </summary>
/// <param name="page">The PDF page.</param>
/// <param name="watermarkResource">The PDF resource that contains watermark.</param>
/// <param name="watermarkImagePadding">The watermark image padding.</param>
/// <param name="watermarkImageAlpha">The watermark image alpha.</param>
/// <param name="ignorePageRotation">Indicates that value of Vintasoft.Imaging.Pdf.Tree.PdfPage.Rotate property should be ignored.</param>
public static void AddWatermarkToPdfPage(
Vintasoft.Imaging.Pdf.Tree.PdfPage page,
Vintasoft.Imaging.Pdf.Tree.PdfResource watermarkResource,
Vintasoft.Imaging.PaddingF watermarkImagePadding,
float watermarkImageAlpha,
bool ignorePageRotation)
{
Vintasoft.Imaging.Pdf.Tree.PdfImageResource watermarkImageResource = watermarkResource as Vintasoft.Imaging.Pdf.Tree.PdfImageResource;
Vintasoft.Imaging.Pdf.Tree.PdfFormXObjectResource watermarkFormResource = watermarkResource as Vintasoft.Imaging.Pdf.Tree.PdfFormXObjectResource;
// gets the size of watermark resource
System.Drawing.SizeF watermarkResourceSize;
if (watermarkImageResource != null)
watermarkResourceSize = new System.Drawing.SizeF(watermarkImageResource.Width, watermarkImageResource.Height);
else
watermarkResourceSize = new System.Drawing.SizeF(watermarkFormResource.BoundingBox.Width, watermarkFormResource.BoundingBox.Height);
// create PDF graphics from PDF page and specify that graphics must clear and add new content
using (Vintasoft.Imaging.Pdf.Drawing.PdfGraphics graphics = Vintasoft.Imaging.Pdf.Drawing.PdfGraphics.FromPage(page))
{
// get mediabox of PDF page
System.Drawing.RectangleF pageMediaBox = page.MediaBox;
// if watermark image must be rotated
if (!ignorePageRotation && page.Rotate != 0)
{
// rotate padding
watermarkImagePadding.Rotate(page.Rotate);
}
// calculate watermark rectangle
System.Drawing.RectangleF watermarkRect = new System.Drawing.RectangleF(
pageMediaBox.X + watermarkImagePadding.Left * pageMediaBox.Width,
pageMediaBox.Y + watermarkImagePadding.Bottom * pageMediaBox.Height,
pageMediaBox.Width - watermarkImagePadding.Horizontal * pageMediaBox.Width,
pageMediaBox.Height - watermarkImagePadding.Vertical * pageMediaBox.Height);
float scale = System.Math.Min(watermarkRect.Width / watermarkResourceSize.Width, watermarkRect.Height / watermarkResourceSize.Height);
System.Drawing.RectangleF watermarkImageRect = new System.Drawing.RectangleF(
watermarkRect.X + (watermarkRect.Width - watermarkResourceSize.Width * scale) / 2,
watermarkRect.Y + (watermarkRect.Height - watermarkResourceSize.Height * scale) / 2,
watermarkResourceSize.Width * scale,
watermarkResourceSize.Height * scale);
// create graphics state parameters
Vintasoft.Imaging.Pdf.Tree.PdfGraphicsStateParameters gsParams = new Vintasoft.Imaging.Pdf.Tree.PdfGraphicsStateParameters(page.Document);
// set blending mode to "Multiply"
gsParams.BlendMode = Vintasoft.Imaging.Pdf.Tree.GraphicsStateBlendMode.Multiply;
// set alpha transparency
gsParams.AlphaForNonStrokingOperations = watermarkImageAlpha;
// save graphics state
graphics.SaveGraphicsState();
// set graphics state parameters
graphics.SetGraphicsStateParameters(gsParams);
// if watermark image must be rotated
if (!ignorePageRotation && page.Rotate != 0)
{
// apply rotation to the PdfGraphics
Vintasoft.Imaging.AffineMatrix matrix = new Vintasoft.Imaging.AffineMatrix();
matrix.RotateAt(
page.Rotate,
watermarkImageRect.X + watermarkImageRect.Width / 2,
watermarkImageRect.Y + watermarkImageRect.Height / 2);
graphics.MultiplyTransform(matrix);
}
// if watermark is an image
if (watermarkImageResource != null)
// draw watermark image
graphics.DrawImage(watermarkImageResource, watermarkImageRect);
else
// draw watermark form
graphics.DrawForm(watermarkFormResource, watermarkImageRect);
// restore graphics state
graphics.RestoreGraphicsState();
}
}
Here is an example of PDF document each page of which contains the added watermark:
testDocument_marked.pdf.
