Watermarks are faded text or images that appear behind the existing content of a document. You can use them to indicate a document's state (confidential, draft, etc.), or add a subtle company logo. A watermark helps prove the origin of a document and discourage unauthorized copies or distribution. In this article, you will learn how to add image watermarks to PDF in C++ using Spire.PDF for C++.
Install Spire.PDF for C++
There are two ways to integrate Spire.PDF for C++ into your application. One way is to install it through NuGet, and the other way is to download the package from our website and copy the libraries into your program. Installation via NuGet is simpler and more recommended. You can find more details by visiting the following link.
Integrate Spire.PDF for C++ in a C++ Application
Add a Single Image Watermark to PDF in C++
The PdfPageBase->GetCanvas()->DrawImage() method provided by Spire.PDF for C++ allows developers to draw images at any position of a PDF page. The image can be faded by adjusting the transparency of the canvas to prevent it from overwriting the text. The detailed steps to add a single image watermark to PDF are as follows.
- Create a PdfDocument object.
- Load a sample PDF document using PdfDocument->LoadFromFile() method.
- Get a specific page from the document using PdfDocument->GetPages()->GetItem() method.
- Set the transparency of the page using PdfPageBase->GetCanvas()->SetTransparency() method.
- Draw an image at the center of the page using PdfPageBase->GetCanvas()->DrawImage() method.
- Save the document to a different PDF file using PdfDocument->SaveToFile() method.
- C++
#include "Spire.Pdf.o.h";
using namespace std;
using namespace Spire::Pdf;
int main()
{
//Specify input file and output file paths
wstring inputFilePath = L"C:\\Users\\Administrator\\Desktop\\sample.pdf";
wstring outputFilePath = L"C:\\Users\\Administrator\\Desktop\\ImageWatermark.pdf";
//Create a PdfDocument object
PdfDocument* doc = new PdfDocument();
//Load a PDF file
doc->LoadFromFile(inputFilePath.c_str());
//Load an image
PdfImage* image = PdfImage::FromFile(L"C:\\Users\\Administrator\\Desktop\\logo.png");
//Get image height and width
int imgHeight = image->GetHeight();
int imgWidth = image->GetWidth();
//Traverse through the pages in the document
for (size_t i = 0; i < doc->GetPages()->GetCount(); i++)
{
//Get a specific page
PdfPageBase* page = doc->GetPages()->GetItem(i);
//Set the page transparency
page->GetCanvas()->SetTransparency(0.5);
//Get the page width and height
float pageWidth = page->GetActualSize()->GetWidth();
float pageHeight = page->GetActualSize()->GetHeight();
//Draw image at the center of the page
RectangleF* rect = new RectangleF((float)(pageWidth - imgWidth) / 2, (float)(pageHeight - imgHeight) / 2, imgWidth, imgHeight);
page->GetCanvas()->DrawImage(image, rect);
}
//Save the document
doc->SaveToFile(outputFilePath.c_str());
doc->Close();
delete doc;
}
Add a Tiled Image Watermark to PDF in C++
A tiled watermark effect can be achieved by using the PdfTilingBrush class. The tiling brush produces a tiled pattern that is repeated to fill a graphics area. The following are the steps to add a tiled image watermark to a PDF document.
- Create a custom method InsertTiledImagetWatermark(PdfPageBase* page, PdfImage* image, int rowNum, int columnNum) to add a tiled watermark to a PDF page. The parameter rowNum and columnNum specify the row number and column number of the tiled watermark.
- Create a PdfDocument object.
- Load a sample PDF document using PdfDocument->LoadFromFile() method.
- Traverse through all pages in the document, and invoke the custom method InsertTiledImageWatermark() to apply watermark to each page.
- Save the document to another file using PdfDocument->SaveToFile() method.
- C++
#include "Spire.Pdf.o.h";
using namespace std;
using namespace Spire::Pdf;
static void InsertTiledImagetWatermark(PdfPageBase* page, PdfImage* image, int rowNum, int columnNum)
{
//Get page height and width
float height = page->GetActualSize()->GetHeight();
float width = page->GetActualSize()->GetWidth();
//Get image heigh and width
float imgHeight = image->GetHeight();
float imgWidth = image->GetWidth();
//Create a tiling brush
PdfTilingBrush* brush = new PdfTilingBrush(new SizeF(width / columnNum, height / rowNum));
//Set transparency
brush->GetGraphics()->SetTransparency(0.5f);
//Translate coordinate system to a certain position
brush->GetGraphics()->TranslateTransform((brush->GetSize()->GetWidth() - imgWidth) / 2, (brush->GetSize()->GetHeight() - imgHeight) / 2);
//Draw image on the brush at the specified coordinates
brush->GetGraphics()->DrawImage(image, 0.0, 0.0);
//Draw rectangle that covers the whole page with the brush
page->GetCanvas()->DrawRectangle(brush, 0, 0, width, height);
}
int main()
{
//Specify input file and output file paths
wstring inputFilePath = L"C:\\Users\\Administrator\\Desktop\\sample.pdf";
wstring outputFilePath = L"C:\\Users\\Administrator\\Desktop\\TiledImageWatermark.pdf";
//Create a PdfDocument object
PdfDocument* doc = new PdfDocument();
//Load a PDF file
doc->LoadFromFile(inputFilePath.c_str());
//Load an image
PdfImage* image = PdfImage::FromFile(L"C:\\Users\\Administrator\\Desktop\\small-logo.png");
//Traverse through the pages in the document
for (size_t i = 0; i < doc->GetPages()->GetCount(); i++)
{
//Get a specific page
PdfPageBase* page = doc->GetPages()->GetItem(i);
//Add tiled image watermark to the page
InsertTiledImagetWatermark(page, image, 4, 4);
}
//Save the document
doc->SaveToFile(outputFilePath.c_str());
doc->Close();
delete doc;
}
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