Watermark Auditing for PDF Compliance Leave feedback

Note

The complete source code for this use case is available on GitHub: groupdocs-watermark/watermark-compliance-assessment-using-groupdocs-watermark-dotnet.

Enterprises that distribute PDF contracts, marketing collateral, or technical manuals often embed watermarks to protect intellectual property and enforce branding rules. Manually opening each file to verify that a specific text watermark (e.g., “Confidential”) appears on every page is error-prone, especially when thousands of documents are involved. This use-case shows how to automate a full-document audit using Watermarker and TextSearchCriteria, confirm that the required watermark exists on every page, verify formatting rules, and produce a concise compliance report.

• .NET runtime 6.0 or newer.
• GroupDocs.Watermark NuGet package (GroupDocs.Watermark).
• A temporary or permanent GroupDocs.Watermark license key (optional for evaluation).
• PDF files located in a local folder that you want to audit.

Add the Watermark package to your project with the .NET CLI:

dotnet add package GroupDocs.Watermark

watermark-audit-tool/
│
├── WatermarkAuditTool/
│   ├── Program.cs
│   ├── WatermarkAuditTool.csproj
│   ├── Resources/
│   │   ├── Logos/
│   │   │   └── expected-logo.png
│   │   └── SampleDocs/
│   │       ├── sample-draft.pdf
│   │       └── sample-watermarked.pdf
│   └── Results/

Below is a step-by-step guide based on the actual Program.cs in the sample repository.

Use the parameterless Search() method on a Watermarker instance to enumerate every watermark, including text, position, rotation, and image data:

using (Watermarker watermarker = new Watermarker(filePath))
{
    PossibleWatermarkCollection watermarks = watermarker.Search();

    foreach (PossibleWatermark wm in watermarks)
    {
        Console.WriteLine($"  Text: {wm.Text ?? "(image)"}");
        Console.WriteLine($"  Position: X={wm.X}, Y={wm.Y}");
        Console.WriteLine($"  Rotation: {wm.RotateAngle} degrees");
        Console.WriteLine($"  Page: {wm.PageNumber}");
    }
}

Build a TextSearchCriteria with SkipUnreadableCharacters enabled to detect obfuscated or fragmented watermarks. The search returns a PASS/FAIL flag:

using (Watermarker watermarker = new Watermarker(filePath))
{
    TextSearchCriteria criteria =
        new TextSearchCriteria(expectedText);
    criteria.SkipUnreadableCharacters = true;

    PossibleWatermarkCollection found = watermarker.Search(criteria);
    bool passed = found.Count > 0;

    Console.WriteLine($"  [{(passed ? "PASS" : "FAIL")}] " +
        $"expected '{expectedText}', " +
        $"found {found.Count} match(es)");
}

Combine TextSearchCriteria with TextFormattingSearchCriteria using the .And() operator to check font, size, and bold style in addition to text presence:

var textCriteria = new TextSearchCriteria(expectedText);

// Check text + font name
var fontCriteria = new TextFormattingSearchCriteria
    { FontName = "Arial" };
CheckRule(watermarker, textCriteria.And(fontCriteria),
    "Font 'Arial'", ref passed, ref failed);

// Check text + minimum font size
var sizeCriteria = new TextFormattingSearchCriteria
    { MinFontSize = 15 };
CheckRule(watermarker, textCriteria.And(sizeCriteria),
    "Min font size >= 15", ref passed, ref failed);

A separate helper verifies page coverage by collecting watermarked page numbers and comparing against the total page count. The final verdict is COMPLIANT or NON-COMPLIANT.

Locate watermarks by old text, clear their FormattedTextFragments, and add new text with updated font and color:

using (Watermarker watermarker = new Watermarker(filePath))
{
    var criteria = new TextSearchCriteria(oldText, false);
    var watermarks = watermarker.Search(criteria);

    foreach (PossibleWatermark wm in watermarks)
    {
        wm.FormattedTextFragments.Clear();
        wm.FormattedTextFragments.Add(
            newText,
            new Font("Arial", 19, FontStyle.Bold),
            Color.DarkBlue,
            Color.Transparent);
    }

    watermarker.Save(outputPath);
}

The screenshot below shows the result — the old watermark text has been replaced with the new text, font, and color:

Note

The sample project also demonstrates adding invisible tracking watermarks for leak detection and recovering them with regex-based TextSearchCriteria. See AddTrackingWatermark and DetectTrackingWatermark in Program.cs.

The RemoveWatermarksByCriteria method in the sample project demonstrates targeted removal — only watermarks matching both text and formatting criteria are deleted:

• The sample works with any document format supported by GroupDocs.Watermark (DOCX, PPTX, etc.). Replace the *.pdf filter with *.* to audit a mixed folder.
• For large collections, consider processing files in parallel (Parallel.ForEach) — the Watermark SDK is thread-safe when each thread uses its own Watermarker instance.
• If you need to audit encrypted PDFs, pass the password to Watermarker via the constructor overload.
• The free evaluation license limits the number of processed pages; acquire a full license for production workloads.

• GroupDocs.Watermark .NET Documentation
• GroupDocs.Watermark .NET API Reference
• Get a Temporary License
• GroupDocs.Watermark Forum