PDF Annotations in .NET with IronPDF

Document review and markup

The most common reach for annotations. A review tool attaches feedback to specific spots and saves a commented copy for the next person, source content unchanged:

using IronPdf;
using IronPdf.Annotations;

var pdf = PdfDocument.FromFile("draft.pdf");
pdf.Annotations.Add(new TextAnnotation(0)
{
    Title = "Reviewer",
    Contents = "Clarify this clause.",
    X = 50,
    Y = 700
});
pdf.SaveAs("draft-reviewed.pdf");

using IronPdf;
using IronPdf.Annotations;

var pdf = PdfDocument.FromFile("draft.pdf");
pdf.Annotations.Add(new TextAnnotation(0)
{
    Title = "Reviewer",
    Contents = "Clarify this clause.",
    X = 50,
    Y = 700
});
pdf.SaveAs("draft-reviewed.pdf");

Imports IronPdf
Imports IronPdf.Annotations

Dim pdf = PdfDocument.FromFile("draft.pdf")
pdf.Annotations.Add(New TextAnnotation(0) With {
    .Title = "Reviewer",
    .Contents = "Clarify this clause.",
    .X = 50,
    .Y = 700
})
pdf.SaveAs("draft-reviewed.pdf")

Contract collaboration without touching the original

Since the annotation layer stays distinct from the contract body, legal teams can leave notes that never alter the binding text. That separation matters wherever the document must stay pristine for audit or signature.

QA flagging on technical documents

An automated check can drop a positioned note wherever it detects a problem (a missing figure, an out-of-spec value), giving a human a clickable map of issues, not a separate report.

Editing through a revision cycle

Existing annotations can be retrieved and updated as feedback changes or notes need repositioning. This supports approval chains, where a supervisor amends reviewer notes before sign-off:

using System.Linq;

var pdf = PdfDocument.FromFile("draft-reviewed.pdf");
var note = (TextAnnotation)pdf.Annotations.First();
note.Contents = "Resolved in v2.";
note.X = 150;
pdf.SaveAs("draft-updated.pdf");

using System.Linq;

var pdf = PdfDocument.FromFile("draft-reviewed.pdf");
var note = (TextAnnotation)pdf.Annotations.First();
note.Contents = "Resolved in v2.";
note.X = 150;
pdf.SaveAs("draft-updated.pdf");

Imports System.Linq

Dim pdf = PdfDocument.FromFile("draft-reviewed.pdf")
Dim note = CType(pdf.Annotations.First(), TextAnnotation)
note.Contents = "Resolved in v2."
note.X = 150
pdf.SaveAs("draft-updated.pdf")

Cleaning up before distribution

Removal is its own use case. Strip internal or outdated comments before a document goes out, so feedback never leaks to an external audience. Use RemoveAt for one, RemoveAllAnnotationsForPage for a page, or Clear for the whole document. This pairs naturally with sanitization or PDF/A export as a finalization step.

Two things that will bite you

PDF coordinates start from the bottom-left corner, not the top-left most UI frameworks use, and are measured in points (1/72 inch); US Letter is 612 x 792, A4 is 595 x 842. Until you account for this, annotations land in the wrong place.

The annotation collection reindexes after each removal. To delete several, work backwards or collect them first and remove in reverse, or you will delete the wrong ones.

What they are, and are not, for

The documented type is TextAnnotation, the sticky note, with properties for title, contents, position, page, subject, icon, and open state. It is not highlight, ink, or stamp markup. Match it to commentary and review, the job it does well, not visual markup it does not claim to do.