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The Syncfusion .NET PDF library supports a wide range of PDF annotations. The library can create, read, delete, and edit annotations. It allows users to annotate PDF with 20+ annotation types with built-in support, or create their own custom annotations. You can annotate PDF in any .NET application like Windows Forms, WPF, ASP.NET (Web forms, MVC, Core), UWP, Xamarin.Forms, Xamarin.Android, and Xamarin.iOS.

Text Markup

Text markup appears as highlight, underline, strikeout, or squiggly underlines in the text of a document with complete customization of color, opacity, border, author, subject. etc.

Text markup in PDF Annotation C#

C# PDF Link annotation

Syncfusion supports web link or URI annotation to add online URI or local link. Document link annotation is used to navigate to a specific destination within the document. File link annotation is used for linking the external files in the PDF.

Rubber Stamp

Syncfusion supports various predefined rubber stamps and custom rubber stamps. Predefined rubber stamps are approved, experimental, not approved, expired, confidential, final, sold, top secret, draft, etc. You can also create custom rubber stamp with text, graphics and images.

Rubber stamp in C# PDF annotation

Popup annotation in C# PDF annotation

You can add text in popup annotation along with other markup annotations. Predefined icons such as comment, help, note etc. are also supported. You can toggle the state of the popups.

File Attachment

File attachment is supported in the Syncfusion Essential PDF library, which is used to link a file embedded to the PDF.

File attachment in C# PDF annotation

C# PDF sound annotation

Sound Annotation

It is also possible to sound files to PDF document using the Syncfusion Essential PDF library to play the sound clip.

Shape Annotation

Include line, square, rectangle, polygon, polyline, ellipse, and circle in the PDF pages to create schematic drawings or to mark important material with the shapes. You can move, resize, remove, or edit the color of the shapes.

.NET pdf Shape annotation

C# pdf Freehand and free text annotation

Freehand and Free Text Annotation

You can comment with ink points or simple text in the PDF page using freehand or ink annotation and free text annotation.

3D Annotation

3D annotations are used to represent 3D artwork in a PDF document. Essential PDF provides support to embed 3D files (u3d) in PDF.

PDF 3D annotation C#

.NET PDF Measurement annotation

Measurement annotation

Essential PDF supports interactive measurement annotations to measure the distance, area, and angle of line segments. The supported measurement annotations are line, square, circle, and angle.

Flatten annotation

The Syncfusion .NET PDF library supports making a PDF annotation non-editable. Flatten PDF annotation will directly write the appearance on a page, but remove the respective annotation. Flattening the popup comment of the annotation is also possible.


The Syncfusion .NET PDF library provides various annotation customizations such as font, color, border style, highlight type, predefined icons, shapes, and more, depending on the annotation type.

Read and modify annotation

Access to read and modify PDF annotation values and properties. You can move annotations around. It is also possible to delete annotations.

Annotation with Layer

It is possible to bind or link all the supported annotations with PDF layers. Toggling, editing, and deleting annotations are also possible with layers.


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Syncfusion’s file format components helped me create the reports I needed, fast. – J. Pereira, Software Developer.

The libraries have been built from scratch and refined for more than a decade to provide blazing-fast performance, comprehensive API, and compatibility across the latest and older versions of these files.

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Syncfusion File Format Libraries - Manipulate Excel, Word, PowerPoint, and PDF files

Read and write Excel, Word, PDF, and PowerPoint files. Also includes integrated visualization capabilities. Advanced features include support for pivot tables, pivot charts, mail-merge, and extensive formatting.


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