How to Edit PDF Document using C#. For further details: https://kb.conholdate.com/total/net/how-to-edit-pdf-document-using-csharp/

how-to-edit-pdf-document-using-csharp.cs

using Aspose.Pdf;
using Aspose.Pdf.Facades;
using Aspose.Pdf.Text;

class Program
{
    static void Main(string[] args) // Edit PDF in C#
    {
        new License().SetLicense("License.lic");

        // Create PdfFileEditor object
        PdfContentEditor editor = new PdfContentEditor();
        editor.BindPdf("Input.pdf");
        // Replace some text in the entire file
        while (true)
            if (editor.ReplaceText("scenario", "situation") == false)
                break;

        // Replace some text and change its font and color
        TextState textState = new TextState();
        textState.ForegroundColor = Color.Red;
        textState.FontSize = 14;

        while (true)
            if (editor.ReplaceText("attack", "fight", textState) == false)
                break;
        System.IO.MemoryStream memoryStream = new System.IO.MemoryStream();
        editor.Save(memoryStream);

        // Add text to an existing page
        PdfFileMend mendor = new PdfFileMend();
        memoryStream.Position = 0;
        mendor.BindPdf(memoryStream);
        FormattedText message = new FormattedText("Test message on the page");
        mendor.AddText(message, 2, 60, 300);
        mendor.Save(memoryStream);

        // Add a paragraph with some text on a new page
        memoryStream.Position = 0;
        Document document = new Document(memoryStream);
        Page page = document.Pages.Add();
        page.Paragraphs.Add(new TextFragment("New paragraph is added"));

        // Save the output
        document.Save("output.pdf");

        System.Console.WriteLine("Done");
    }
}