How to redact PDF content in C#

Mark exact text and apply redaction

This example removes one exact text match from supported page content, adds overlay text, and saves the result as a rewritten file.

using var pdf = Pdf.Load(File.OpenRead("input.pdf"));

var plan = await pdf.RedactionAsync();

await plan.MarkTextAsync("12345");

await plan.ApplyAsync(new PdfRedactionOptions
{
    OverlayText = "REDACTED"
});

await pdf.SaveAsync(File.Create("redacted.pdf"));

Match text with a regular expression

Use the regex overload when the content follows a known pattern, such as identifiers or account numbers.

using System.Text.RegularExpressions;

await plan.MarkTextAsync(
    new Regex(@"\b\d{3}-\d{2}-\d{4}\b"));

Mark an explicit region on a page

Use region marks when you already know the page and rectangle that should be removed.

plan.MarkRegion(
    1,
    Rectangle.FromCoordinates(
        new Coordinate(72, 520),
        new Coordinate(180, 548)));

Redaction uses rewritten-file save behavior

ApplyAsync(...) opts into RemoveHistoryAsync() before you save, so earlier incremental revisions are not preserved in the output file.

await plan.ApplyAsync(new PdfRedactionOptions
{
    FillColor = RGBColour.Black,
    OverlayText = "REDACTED"
});

await pdf.SaveAsync(File.Create("redacted.pdf"));

Current limits

This version removes matched text from supported page content and structurally redacts intersecting vector paths, image XObjects, and form XObjects. It still refuses inline images and shading content, and it does not yet derive OCR bounds for scanned pages.