Explore the Best Alternatives for PDFsharp Add Watermark to PDF

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, and are closely related to text and image stamps used for document annotation.

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.

IronPDF

IronPDF is a premium, feature-rich .NET library designed to streamline PDF handling, from creating PDFs from scratch to advanced manipulation tasks. 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

PDFsharp is an open-source library that allows developers to create, edit, and manipulate PDFs in C#. If you are currently using PDFsharp and considering a switch, the PDFsharp to IronPDF migration guide walks through the transition process. It offers fine-grained control over drawing operations, though watermarking involves more manual implementation than IronPDF's abstracted approach.

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).
• Does not include built-in high-level watermarking functions; developers implement features like opacity and rotation directly through the drawing API.

Here is a quick side-by-side summary of how the two libraries compare for watermarking tasks:

IronPDF's free 30-day trial includes the full watermarking API used in the examples below.

Text Watermark Example

using IronPdf;

const string filename = "existing.pdf";
// Load the existing PDF file
PdfDocument pdf = PdfDocument.FromFile(filename);

// Create a simple HTML-based watermark
string watermark = "<h1 style='color:red'>Confidential!</h1>";

// Apply the watermark to the PDF
pdf.ApplyWatermark(watermark);

// Save the updated document with the applied watermark
pdf.SaveAs("watermarked.pdf");

using IronPdf;

const string filename = "existing.pdf";
// Load the existing PDF file
PdfDocument pdf = PdfDocument.FromFile(filename);

// Create a simple HTML-based watermark
string watermark = "<h1 style='color:red'>Confidential!</h1>";

// Apply the watermark to the PDF
pdf.ApplyWatermark(watermark);

// Save the updated document with the applied 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 load the existing PDF using the FromFile method. Then, we create a simple string formatted as an HTML element as the watermark and apply it to the PDF using ApplyWatermark, similar to how you would use HTML to create a PDF from scratch. As shown in the output image, this has added a simple text string "Confidential" as a watermark on our PDF.

Image Watermark Example

using IronPdf;

// Load the PDF document
PdfDocument pdf = PdfDocument.FromFile("existing.pdf");

// Create an HTML-based watermark containing the image
string watermark = "<img src='https://ironsoftware.com/img/products/ironpdf-logo-text-dotnet.svg'>";

// Apply the watermark to the PDF with rotation and opacity
pdf.ApplyWatermark(watermark, rotation: 45, opacity: 80);

// Save the watermarked document
pdf.SaveAs("watermarked.pdf");

using IronPdf;

// Load the PDF document
PdfDocument pdf = PdfDocument.FromFile("existing.pdf");

// Create an HTML-based watermark containing the image
string watermark = "<img src='https://ironsoftware.com/img/products/ironpdf-logo-text-dotnet.svg'>";

// Apply the watermark to the PDF with rotation and opacity
pdf.ApplyWatermark(watermark, rotation: 45, opacity: 80);

// Save the watermarked document
pdf.SaveAs("watermarked.pdf");

Adding an image as a watermark is just as easy as adding text, as they both use the same method. Just like in the text example, we create a new watermark string variable containing the HTML image tag pointing to the image URL and apply it. This time, we include customized rotation and opacity transformations via IronPDF's rendering options parameters.

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

Text Watermark Example

using PdfSharp.Pdf;
using PdfSharp.Drawing;
using PdfSharp.Pdf.IO;

const string filename = "existing.pdf";
// Open the PDF document in modify mode
var document = PdfReader.Open(filename, PdfDocumentOpenMode.Modify);

foreach (var page in document.Pages)
{
    // Create an XGraphics object for drawing
    var gfx = XGraphics.FromPdfPage(page);

    // Move the origin to the center of the page for rotation purposes
    gfx.TranslateTransform(page.Width / 2, page.Height / 2);

    // Rotate for diagonal watermark placement
    gfx.RotateTransform(Math.Atan(page.Height / page.Width));

    // Define font and brush for drawing the watermark text
    var font = new XFont("Arial", 40);
    var brush = new XSolidBrush(XColor.FromArgb(128, XColors.Red));  // Semi-transparent red

    // Draw the watermark text centered on the page
    gfx.DrawString("WATERMARK", font, brush, new XPoint(0, 0));
}

// Save modified document
document.Save("watermarked.pdf");

using PdfSharp.Pdf;
using PdfSharp.Drawing;
using PdfSharp.Pdf.IO;

const string filename = "existing.pdf";
// Open the PDF document in modify mode
var document = PdfReader.Open(filename, PdfDocumentOpenMode.Modify);

foreach (var page in document.Pages)
{
    // Create an XGraphics object for drawing
    var gfx = XGraphics.FromPdfPage(page);

    // Move the origin to the center of the page for rotation purposes
    gfx.TranslateTransform(page.Width / 2, page.Height / 2);

    // Rotate for diagonal watermark placement
    gfx.RotateTransform(Math.Atan(page.Height / page.Width));

    // Define font and brush for drawing the watermark text
    var font = new XFont("Arial", 40);
    var brush = new XSolidBrush(XColor.FromArgb(128, XColors.Red));  // Semi-transparent red

    // Draw the watermark text centered on the page
    gfx.DrawString("WATERMARK", font, brush, new XPoint(0, 0));
}

// Save modified document
document.Save("watermarked.pdf");

This implementation draws a watermark on each page through explicit coordinate-based positioning. While it produces a similar output to the IronPDF example, PDFsharp's approach involves more code — IronPDF's text watermark requires roughly 4 active lines versus PDFsharp's 10, since PDFsharp delegates layout decisions (translation, rotation, font selection) to the developer rather than abstracting them.

Image Watermark Example

using PdfSharp.Pdf;
using PdfSharp.Drawing;
using PdfSharp.Pdf.IO;

// Open the existing PDF document in modify mode
var document = PdfReader.Open("sample.pdf", PdfDocumentOpenMode.Modify);

// Load the watermark image
XImage watermark = XImage.FromFile("watermark.png");

foreach (var page in document.Pages)
{
    // Create a graphics object from the page
    XGraphics gfx = XGraphics.FromPdfPage(page);

    // Draw the image watermark at the specified position and size
    gfx.DrawImage(watermark, 50, 100, watermark.PixelWidth / 2, watermark.PixelHeight / 2);
}

// Save the modified PDF document
document.Save("watermarked.pdf");

using PdfSharp.Pdf;
using PdfSharp.Drawing;
using PdfSharp.Pdf.IO;

// Open the existing PDF document in modify mode
var document = PdfReader.Open("sample.pdf", PdfDocumentOpenMode.Modify);

// Load the watermark image
XImage watermark = XImage.FromFile("watermark.png");

foreach (var page in document.Pages)
{
    // Create a graphics object from the page
    XGraphics gfx = XGraphics.FromPdfPage(page);

    // Draw the image watermark at the specified position and size
    gfx.DrawImage(watermark, 50, 100, watermark.PixelWidth / 2, watermark.PixelHeight / 2);
}

// Save the modified PDF document
document.Save("watermarked.pdf");

This method places an image watermark at a fixed position and size. Opacity handling is outside PDFsharp's single-call API surface — developers who need transparency control manage it through the XGraphics pipeline directly. As with the text watermark example, PDFsharp gives you granular control over rendering at the cost of additional setup compared to IronPDF's higher-level watermarking API.

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: Ships as a single NuGet package with watermark operations that handle opacity, rotation, and positioning in one method call, reducing per-page processing overhead when watermarking multi-page documents. For large-scale workflows, see the IronPDF performance optimization guide.
• PDFSharp: Lightweight with a small dependency footprint. For complex watermarking tasks involving multiple transformations per page, developers may need to profile and optimize their drawing logic, since PDFsharp does not batch or cache these operations internally.

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). Some newer framework features may be outside its current scope, depending on the community port you select.

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.

Beyond license cost, total project cost includes the developer hours spent on manual coordinate-based positioning, custom opacity and rotation logic, and per-page drawing code that IronPDF handles in a single method call. For teams evaluating cost over a multi-year project lifecycle, these implementation and maintenance hours frequently eclipse the difference between open-source and commercial licensing.