IronSoftware

Posted on Jan 12

PDF Annotations in C# (.NET Guide)

#dotnet #csharp

PDF annotations are sticky notes, highlights, and comments attached to specific locations in a document. They're essential for document review workflows—letting reviewers mark up PDFs without altering the original content.

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("document.pdf");

var annotation = new PdfAnnotation(0, 100, 100)
{
    Title = "Review Note",
    Contents = "Please verify this section.",
    Icon = PdfAnnotationIcon.Comment
};

pdf.Annotations.Add(annotation);
pdf.SaveAs("annotated.pdf");

IronPDF makes adding annotations straightforward—just specify where and what to say.

What Types of Annotations Can I Add?

PDF annotations come in several varieties:

Type	Purpose
Text (Sticky Note)	Comments anchored to a point
Highlight	Mark up existing text
Underline	Emphasize text
Strikeout	Mark text for deletion
Link	Clickable navigation
Stamp	Visual markers (Approved, Draft, etc.)

IronPDF's PdfAnnotation class handles text annotations. For stamps and visual elements, use the stamping features.

How Do I Add a Text Annotation?

Text annotations appear as icons that expand when clicked:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("contract.pdf");

// Create annotation at position (200, 300) on page 0
var annotation = new PdfAnnotation(
    pageIndex: 0,
    x: 200,
    y: 300)
{
    Title = "Legal Review",
    Contents = "This clause needs revision. See comments from legal team.",
    Icon = PdfAnnotationIcon.Comment,
    Opacity = 0.9,
    Printable = true,
    Hidden = false,
    Open = false  // Collapsed by default
};

pdf.Annotations.Add(annotation);
pdf.SaveAs("contract-reviewed.pdf");

Coordinates are in points (72 points = 1 inch) from the bottom-left corner.

What Annotation Icons Are Available?

IronPDF supports standard PDF annotation icons:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("document.pdf");

// Different icon types for different purposes
var comment = new PdfAnnotation(0, 100, 700)
{
    Title = "Comment",
    Contents = "General feedback",
    Icon = PdfAnnotationIcon.Comment
};

var help = new PdfAnnotation(0, 150, 700)
{
    Title = "Question",
    Contents = "Clarification needed here",
    Icon = PdfAnnotationIcon.Help
};

var note = new PdfAnnotation(0, 200, 700)
{
    Title = "Note",
    Contents = "Important information",
    Icon = PdfAnnotationIcon.Note
};

var insert = new PdfAnnotation(0, 250, 700)
{
    Title = "Insert",
    Contents = "Add text here",
    Icon = PdfAnnotationIcon.Insert
};

pdf.Annotations.Add(comment);
pdf.Annotations.Add(help);
pdf.Annotations.Add(note);
pdf.Annotations.Add(insert);

pdf.SaveAs("multi-annotated.pdf");

Icons provide visual cues about the annotation's purpose.

How Do I Control Annotation Appearance?

Customize color, opacity, and visibility:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("report.pdf");

var annotation = new PdfAnnotation(0, 300, 500)
{
    Title = "Important",
    Contents = "This data requires verification",
    Icon = PdfAnnotationIcon.Note,

    // Appearance settings
    Opacity = 0.75,           // 75% opaque
    Printable = true,         // Show when printed
    Hidden = false,           // Visible on screen
    Open = true,              // Expanded by default
    ReadOnly = false,         // Can be edited
    Subject = "Data Review"   // Category/subject
};

pdf.Annotations.Add(annotation);
pdf.SaveAs("styled-annotation.pdf");

The Printable property is useful—sometimes you want annotations visible on screen but not in printed copies.

How Do I Read Existing Annotations?

Retrieve annotations from a PDF:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("annotated-document.pdf");

// Get all annotations
var annotations = pdf.Annotations;

Console.WriteLine($"Found {annotations.Count} annotations");

foreach (var annotation in annotations)
{
    Console.WriteLine($"Page: {annotation.PageIndex}");
    Console.WriteLine($"Title: {annotation.Title}");
    Console.WriteLine($"Contents: {annotation.Contents}");
    Console.WriteLine($"Position: ({annotation.X}, {annotation.Y})");
    Console.WriteLine("---");
}

Useful for extracting review comments or generating annotation reports.

How Do I Edit Annotations?

Modify existing annotations:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("reviewed.pdf");

// Get annotations
var annotations = pdf.Annotations;

// Edit first annotation
if (annotations.Count > 0)
{
    var first = annotations[0];
    first.Contents = "Updated: This issue has been resolved.";
    first.Title = "Resolved";
}

// Edit all annotations matching criteria
foreach (var annotation in annotations)
{
    if (annotation.Title == "Review Note")
    {
        annotation.Title = "Addressed";
        annotation.Contents += "\n[Status: Complete]";
    }
}

pdf.SaveAs("updated-annotations.pdf");

How Do I Remove Annotations?

Delete specific or all annotations:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("annotated.pdf");

// Remove a specific annotation by index
pdf.Annotations.RemoveAt(0);

// Or remove all annotations
pdf.Annotations.Clear();

pdf.SaveAs("clean.pdf");

For selective removal:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("document.pdf");

// Remove annotations by criteria
var toRemove = pdf.Annotations
    .Where(a => a.Title == "Draft" || a.PageIndex == 0)
    .ToList();

foreach (var annotation in toRemove)
{
    pdf.Annotations.Remove(annotation);
}

pdf.SaveAs("filtered.pdf");

How Do I Add Annotations to Specific Pages?

Target annotations to particular pages:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("multipage.pdf");

// Annotation on first page (index 0)
pdf.Annotations.Add(new PdfAnnotation(0, 100, 700)
{
    Title = "Introduction",
    Contents = "Good overview"
});

// Annotation on third page (index 2)
pdf.Annotations.Add(new PdfAnnotation(2, 100, 700)
{
    Title = "Analysis",
    Contents = "Numbers need verification"
});

// Annotation on last page
int lastPage = pdf.PageCount - 1;
pdf.Annotations.Add(new PdfAnnotation(lastPage, 100, 700)
{
    Title = "Conclusion",
    Contents = "Strong summary"
});

pdf.SaveAs("page-annotated.pdf");

How Do I Create a Document Review Workflow?

Build a practical review system:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

public class DocumentReviewer
{
    public void AddReviewComment(PdfDocument pdf, int page,
        double x, double y, string reviewer, string comment)
    {
        var annotation = new PdfAnnotation(page, x, y)
        {
            Title = $"Review by {reviewer}",
            Contents = comment,
            Icon = PdfAnnotationIcon.Comment,
            Subject = "Review Comment",
            Printable = false  // Don't print review comments
        };

        pdf.Annotations.Add(annotation);
    }

    public void MarkAsApproved(PdfDocument pdf, int page)
    {
        var approval = new PdfAnnotation(page, 450, 750)
        {
            Title = "Status",
            Contents = $"Approved on {DateTime.Now:yyyy-MM-dd}",
            Icon = PdfAnnotationIcon.Check,
            Printable = true
        };

        pdf.Annotations.Add(approval);
    }

    public List<string> GetAllComments(PdfDocument pdf)
    {
        return pdf.Annotations
            .Where(a => a.Subject == "Review Comment")
            .Select(a => $"Page {a.PageIndex + 1}: {a.Contents}")
            .ToList();
    }
}

// Usage
var pdf = PdfDocument.FromFile("draft.pdf");
var reviewer = new DocumentReviewer();

reviewer.AddReviewComment(pdf, 0, 200, 500, "John", "Good introduction");
reviewer.AddReviewComment(pdf, 2, 150, 400, "Jane", "Check these figures");
reviewer.MarkAsApproved(pdf, pdf.PageCount - 1);

pdf.SaveAs("reviewed-draft.pdf");

How Do I Export Annotations?

Extract annotations for external processing:

using IronPdf;
using System.Text.Json;
// Install via NuGet: Install-Package IronPdf

var pdf = PdfDocument.FromFile("reviewed.pdf");

var exportData = pdf.Annotations.Select(a => new
{
    Page = a.PageIndex + 1,
    Position = new { X = a.X, Y = a.Y },
    Title = a.Title,
    Content = a.Contents,
    Subject = a.Subject
}).ToList();

var json = JsonSerializer.Serialize(exportData, new JsonSerializerOptions
{
    WriteIndented = true
});

File.WriteAllText("annotations.json", json);
Console.WriteLine($"Exported {exportData.Count} annotations");

How Do I Add Annotations During PDF Creation?

Add annotations while generating PDFs:

using IronPdf;
// Install via NuGet: Install-Package IronPdf

var renderer = new [ChromePdfRenderer](https://ironpdf.com/blog/videos/how-to-render-webgl-sites-to-pdf-in-csharp-ironpdf/)();
var pdf = renderer.RenderHtmlAsPdf(@"
    <h1>Project Proposal</h1>
    <p>This document outlines the project scope...</p>
    <h2>Budget</h2>
    <p>Total estimated cost: $50,000</p>
");

// Add annotations to the freshly created PDF
pdf.Annotations.Add(new PdfAnnotation(0, 100, 600)
{
    Title = "Author Note",
    Contents = "Budget figures are preliminary estimates",
    Icon = PdfAnnotationIcon.Note
});

pdf.SaveAs("proposal-with-notes.pdf");

Quick Reference

Operation	Code
Add annotation	`pdf.Annotations.Add(new PdfAnnotation(...))`
Get count	`pdf.Annotations.Count`
Access by index	`pdf.Annotations[0]`
Remove specific	`pdf.Annotations.RemoveAt(index)`
Remove all	`pdf.Annotations.Clear()`
Iterate	`foreach (var a in pdf.Annotations)`

Property	Purpose
`PageIndex`	Which page (0-based)
`X`, `Y`	Position in points
`Title`	Annotation header
`Contents`	Main text
`Icon`	Visual icon type
`Opacity`	Transparency (0-1)
`Printable`	Include when printing
`Open`	Expanded by default

PDF annotations transform static documents into collaborative review tools. Add them programmatically to automate document workflows.

For more annotation options, see the IronPDF annotations documentation.

Written by Jacob Mellor, CTO at Iron Software. Jacob created IronPDF and leads a team of 50+ engineers building .NET document processing libraries.

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