Explore the Best Alternatives for PDFsharp Add Watermark to PDF

Adding watermarks to PDFs is a common requirement for document security, branding, and version control. Whether marking documents as confidential, branding official reports, or preventing unauthorized reproduction, watermarking is an essential feature.

In C#, developers have multiple libraries to choose from, with IronPDF and PDFSharp being two of the most popular options. However, their approaches, ease of use, performance, and licensing structures differ significantly. This article provides a detailed comparison between IronPDF and PDFsharp for adding watermarks to existing PDFs, offering insights into their functionalities, implementation processes, and customization capabilities.

By the end of this article, you will have a clear understanding of which library best suits your project’s needs based on ease of use, performance, and feature availability.

Understanding PDF Watermarking

What is a Watermark?

A watermark is a graphical or textual overlay on a document that serves as an identifier, deterrent, or branding element. Watermarks can be visible or invisible, depending on their purpose.

Types of Watermarks

• Text Watermark – Typically a semi-transparent overlay with a message like "CONFIDENTIAL" or "DRAFT."
• Image Watermark – A logo, emblem, or graphic embedded into the document.
• Transparent Watermark – A subtle branding mark that doesn’t obstruct the document’s readability.
• Stamped Watermark – A more prominent, bold marking that ensures visibility.

Common Use Cases

• Security & Protection – Prevent unauthorized duplication by marking documents as proprietary.
• Branding – Add company logos or signatures to maintain brand consistency across documents.
• Version Control – Label drafts, final versions, or document revisions.

Overview of IronPDF and PDFsharp

IronPDF

Broken image Add from Pixabay, select from your files or drag and drop an image here.

IronPDF is a premium, feature-rich .NET library designed to streamline PDF handling. It is especially useful for developers looking for easy implementation of PDF manipulation tasks, including watermarking.

Key Features:

• Simple and intuitive API requiring minimal code.
• Supports text and image watermarks with customization options.
• Offers opacity control, positioning, and rotation for precise placement.
• Compatible with .NET 6+, .NET Core, and .NET Framework.
• Available with a perpetual licensing model for long-term use.
• Additional capabilities include PDF annotations, HTML-to-PDF conversion, and digital signatures.

PDFsharp

Broken image Add from Pixabay, select from your files or drag and drop an image here.

PDFsharp is an open-source library that allows developers to create, edit, and manipulate PDFs in C#. While it is highly flexible, watermarking requires more manual effort compared to IronPDF.

Key Features:

• Free and open-source, making it cost-effective for budget-conscious projects.
• Provides low-level control over PDF drawing operations, including both outlined graphical paths and transparent graphical paths.
• Supports both text and image watermarks but requires additional code for transformations.
• Works with .NET Framework and .NET Core (via PDFSharpCore).
• Lacks built-in high-level watermarking functions, requiring developers to manually implement features like opacity and rotation.

Adding a Watermark with IronPDF

IronPDF provides a simple API that enables developers to apply watermarks efficiently with just a few lines of code, making it easy to streamline your PDF watermarking tasks efficiently, without any complex or manual setups. IronPDF's watermark tool can use HTML/CSS strings for the watermark, as you will see below, giving you full control over how your watermark will appear.

Text Watermark Example

using IronPdf;
const string filename = "existing.pdf";
PdfDocument pdf = PdfDocument.FromFile(filename);
string watermark = "<h1 style='color:red'>Confidential!</h1>";
pdf.ApplyWatermark(watermark);
pdf.SaveAs("watermarked.pdf");

using IronPdf;
const string filename = "existing.pdf";
PdfDocument pdf = PdfDocument.FromFile(filename);
string watermark = "<h1 style='color:red'>Confidential!</h1>";
pdf.ApplyWatermark(watermark);
pdf.SaveAs("watermarked.pdf");

Imports IronPdf
Private Const filename As String = "existing.pdf"
Private pdf As PdfDocument = PdfDocument.FromFile(filename)
Private watermark As String = "<h1 style='color:red'>Confidential!</h1>"
pdf.ApplyWatermark(watermark)
pdf.SaveAs("watermarked.pdf")

In this code example, we see just how easy it is to apply a watermark to your existing PDF files with IronPDF. Here, we have loaded in the existing PDF using the FromFile method. Then, we create a simple string format watermark, and apply it to the PDF using ApplyWatermark. As you can see in the output image, this has added a simple text string "Confidential" as a watermark on our PDF.

Image Watermark Example

using IronPdf;
PdfDocument pdf = PdfDocument.FromFile("existing.pdf");
string watermark = "<img src='https://ironsoftware.com/img/products/ironpdf-logo-text-dotnet.svg'>";
pdf.ApplyWatermark(watermark, rotation: 45, opacity: 80);
pdf.SaveAs("watermarked.pdf");

using IronPdf;
PdfDocument pdf = PdfDocument.FromFile("existing.pdf");
string watermark = "<img src='https://ironsoftware.com/img/products/ironpdf-logo-text-dotnet.svg'>";
pdf.ApplyWatermark(watermark, rotation: 45, opacity: 80);
pdf.SaveAs("watermarked.pdf");

Imports IronPdf
Private pdf As PdfDocument = PdfDocument.FromFile("existing.pdf")
Private watermark As String = "<img src='https://ironsoftware.com/img/products/ironpdf-logo-text-dotnet.svg'>"
pdf.ApplyWatermark(watermark, rotation:= 45, opacity:= 80)
pdf.SaveAs("watermarked.pdf")

Adding an image as a watermark is just as easy as adding text, as they both use the same method. Much like in the text example, we simply create a new watermark string variable, containing the content we want to use as the watermark (in this case our image), and we apply it like before. This time, we have added in a customized rotation transformation and opacity.

This approach overlays an image watermark at a specified position, allowing for custom placement and transparency.

Adding a Watermark with PDFsharp

PDFsharp requires developers to manually render text and images using its GDI+ drawing API. To watermark an existing PDF file, create an XGraphics object for drawing and apply the desired content.

Text Watermark Example

using PdfSharp.Pdf;
using PdfSharp.Drawing;
using PdfSharp.Pdf.IO;
const string filename = "existing.pdf";
var document = PdfReader.Open(filename, PdfDocumentOpenMode.Modify);
foreach (var page in document.Pages)
{
    var gfx = XGraphics.FromPdfPage(page); // get an XGraphics object
    gfx.TranslateTransform(page.Width / 2, page.Height / 2);
    gfx.RotateTransform(Math.Atan(page.Height / page.Width)); // Rotate for diagonal watermark
    var font = new XFont("Arial", 40);
    var brush = new XSolidBrush(XColor.FromArgb(128, XColors.Red));
    gfx.DrawString("WATERMARK", font, brush, new XPoint(0, 0)); // Drawing beneath the existing content
}
document.Save("watermarked.pdf");

using PdfSharp.Pdf;
using PdfSharp.Drawing;
using PdfSharp.Pdf.IO;
const string filename = "existing.pdf";
var document = PdfReader.Open(filename, PdfDocumentOpenMode.Modify);
foreach (var page in document.Pages)
{
    var gfx = XGraphics.FromPdfPage(page); // get an XGraphics object
    gfx.TranslateTransform(page.Width / 2, page.Height / 2);
    gfx.RotateTransform(Math.Atan(page.Height / page.Width)); // Rotate for diagonal watermark
    var font = new XFont("Arial", 40);
    var brush = new XSolidBrush(XColor.FromArgb(128, XColors.Red));
    gfx.DrawString("WATERMARK", font, brush, new XPoint(0, 0)); // Drawing beneath the existing content
}
document.Save("watermarked.pdf");

Imports PdfSharp.Pdf
Imports PdfSharp.Drawing
Imports PdfSharp.Pdf.IO
Private Const filename As String = "existing.pdf"
Private document = PdfReader.Open(filename, PdfDocumentOpenMode.Modify)
For Each page In document.Pages
	Dim gfx = XGraphics.FromPdfPage(page) ' get an XGraphics object
	gfx.TranslateTransform(page.Width \ 2, page.Height \ 2)
	gfx.RotateTransform(Math.Atan(page.Height \ page.Width)) ' Rotate for diagonal watermark
	Dim font = New XFont("Arial", 40)
	Dim brush = New XSolidBrush(XColor.FromArgb(128, XColors.Red))
	gfx.DrawString("WATERMARK", font, brush, New XPoint(0, 0)) ' Drawing beneath the existing content
Next page
document.Save("watermarked.pdf")

Broken image Add from Pixabay, select from your files or drag and drop an image here.

This implementation manually draws a watermark on each page, requiring precise positioning and customization. While it's capable of handling the task with a similar output to the IronPDF example, PDFsharp requires more code, and has a more complex method, to handle applying text watermarks to existing content or new PDF files.

Image Watermark Example

using PdfSharp.Pdf;
using PdfSharp.Drawing;
var document = PdfReader.Open("sample.pdf", PdfDocumentOpenMode.Modify);
XImage watermark = XImage.FromFile("watermark.png");
foreach (var page in document.Pages)
{
    XGraphics gfx = XGraphics.FromPdfPage(page);
    gfx.DrawImage(watermark, 50, 100, watermark.PixelWidth / 2, watermark.PixelHeight / 2);
}
document.Save("watermarked.pdf");

using PdfSharp.Pdf;
using PdfSharp.Drawing;
var document = PdfReader.Open("sample.pdf", PdfDocumentOpenMode.Modify);
XImage watermark = XImage.FromFile("watermark.png");
foreach (var page in document.Pages)
{
    XGraphics gfx = XGraphics.FromPdfPage(page);
    gfx.DrawImage(watermark, 50, 100, watermark.PixelWidth / 2, watermark.PixelHeight / 2);
}
document.Save("watermarked.pdf");

Imports PdfSharp.Pdf
Imports PdfSharp.Drawing
Private document = PdfReader.Open("sample.pdf", PdfDocumentOpenMode.Modify)
Private watermark As XImage = XImage.FromFile("watermark.png")
For Each page In document.Pages
	Dim gfx As XGraphics = XGraphics.FromPdfPage(page)
'INSTANT VB WARNING: Instant VB cannot determine whether both operands of this division are integer types - if they are then you should use the VB integer division operator:
	gfx.DrawImage(watermark, 50, 100, watermark.PixelWidth / 2, watermark.PixelHeight / 2)
Next page
document.Save("watermarked.pdf")

This method places an image watermark, but unlike IronPDF, opacity must be handled separately. Much like with the text watermark example, applying an image-based watermark onto an existing PDF with PDFsharp requires a more elaborate, complex setup when compared to IronPDF's streamlined watermarking API.

Comparing IronPDF and PDFsharp for Watermarking

Ease of Use

• IronPDF: Provides high-level functions that simplify watermarking with minimal code. It abstracts complex operations, making it ideal for developers who need a quick and efficient solution.
• PDFSharp: Requires manual implementation using the graphics API, which increases complexity and development time. It is better suited for developers who need fine-grained control over rendering but are comfortable with additional coding.

Performance

• IronPDF: Optimized for high-speed PDF processing, capable of handling large documents efficiently without significant performance degradation.
• PDFSharp: While lightweight, it may require additional optimizations for handling large PDFs. Complex watermarking tasks with multiple transformations can lead to slower performance compared to IronPDF.

Customization Options

• IronPDF: Built-in support for opacity, rotation, positioning, and font size customization. Users can easily tweak settings without delving into complex rendering logic.
• PDFSharp: Requires additional coding for opacity, transparency effects, and transformation handling. While powerful, it demands a higher level of customization from the developer, including using the var format for specific rendering tasks.

Compatibility

• IronPDF: Fully compatible with .NET 6+, .NET Core, and .NET Framework, making it suitable for modern and legacy applications.
• PDFSharp: Supports .NET Framework and .NET Core (via PDFSharpCore), but may lack certain modern features available in newer frameworks.

Licensing and Cost

• IronPDF: A commercial product that requires a paid license but includes perpetual licensing options, customer support, and continuous updates.
• PDFSharp: Open-source and free to use, making it a cost-effective solution for developers who prefer an unrestricted licensing model but are willing to handle their own support and updates.

Conclusion

For developers who need an easy and efficient way to watermark PDFs, IronPDF is the superior choice due to its user-friendly API and built-in features. However, if budget constraints are a concern and you don’t mind writing additional code, PDFSharp is a solid open-source alternative. Ultimately, the best choice depends on your project requirements, coding expertise, and available resources.

🚀Try IronPDF out for yourself by downloading the free trial and exploring how it can take your C# PDF projects to the next level today!