Remove watermark from photo | https://docs.conholdate.com/net/removing-watermark-from-photo/

RemoveHyperlinksWithParticularUrl.cs

// Constants.InDocumentPdf is an absolute or relative path to your document. Ex: @"C:\Docs\document.pdf"
using (Watermarker watermarker = new Watermarker(Constants.InDocumentPdf))
{
    PossibleWatermarkCollection watermarks = watermarker.Search(new TextSearchCriteria(new Regex(@"someurl\.com")));
    for (int i = watermarks.Count - 1; i >= 0; i--)
    {
        // Ensure that only hyperlinks will be removed.
        if (watermarks[i] is HyperlinkPossibleWatermark)
        {
            // Output the full url of the hyperlink
            Console.WriteLine(watermarks[i].Text);

            // Remove hyperlink from the document
            watermarks.RemoveAt(i);
        }
    }

    watermarker.Save(Constants.OutDocumentPdf);
}

RemoveWatermark.cs

// Constants.InDocumentPdf is an absolute or relative path to your document. Ex: @"C:\Docs\document.pdf"
using (Watermarker watermarker = new Watermarker(Constants.InDocumentPdf))
{
    PossibleWatermarkCollection possibleWatermarks = watermarker.Search();

    // Remove possible watermark at the specified index from the document.
    possibleWatermarks.RemoveAt(0);

    // Remove specified possible watermark from the document.
    possibleWatermarks.Remove(possibleWatermarks[0]);

    watermarker.Save(Constants.OutDocumentPdf);
}

RemoveWatermarkWithParticularTextFormatting.cs

// Constants.InDocumentPdf is an absolute or relative path to your document. Ex: @"C:\Docs\document.pdf"
using (Watermarker watermarker = new Watermarker(Constants.InDocumentPdf))
{
    TextFormattingSearchCriteria criteria = new TextFormattingSearchCriteria();
    criteria.ForegroundColorRange = new ColorRange();
    criteria.ForegroundColorRange.MinHue = -5;
    criteria.ForegroundColorRange.MaxHue = 10;
    criteria.ForegroundColorRange.MinBrightness = 0.01f;
    criteria.ForegroundColorRange.MaxBrightness = 0.99f;
    criteria.BackgroundColorRange = new ColorRange();
    criteria.BackgroundColorRange.IsEmpty = true;
    criteria.FontName = "Arial";
    criteria.MinFontSize = 19;
    criteria.MaxFontSize = 42;
    criteria.FontBold = true;

    PossibleWatermarkCollection watermarks = watermarker.Search(criteria);
    watermarks.Clear();

    watermarker.Save(Constants.OutDocumentPdf);
}

Read the complete article: https://docs.conholdate.com/net/removing-watermark-from-photo/