Biblioteca PDF para C# y VB.NET

using (var merged = new PdfDocument("first.pdf"))
{
    merged.Append("second.pdf");
    merged.ReplaceDuplicateObjects();
    merged.Save("merged.pdf");

    // copiar la tercera y la primera página a un nuevo documento PDF
    using (PdfDocument splitted = pdf.CopyPages(new[] { 2, 0 }))
    {
        splitted.RemoveUnusedResources();
        splitted.Save("splitted.pdf");
    }
}

using (var converter = await HtmlConverter.CreateAsync())
{
    var options = new HtmlConversionOptions();

    options.Page.SetSize(PdfPaperSize.A5, isLandscape: true);
    options.Page.MarginTop = 50;
    options.Page.MarginBottom = 50;

    options.Start.SetStartAfterDelay(10 * 1000);

    options.Authentication.SetCredentials("name", "password");

    options.CustomUserAgent = "A user agent of your app";

    using (var pdf = await converter.CreatePdfAsync(url, options))
        pdf.Save("output.pdf");
}

PdfDocumentBuilder
    .Create()
    .Generate("table.pdf", doc => doc.Pages(page =>
    {
        page.Content().Table(t =>
        {
            t.Columns(c =>
            {
                c.RelativeColumn(1);
                c.RelativeColumn(2);
            });

            t.Header(h =>
            {
                h.Cell().Text("Add-on");
                h.Cell().Text("Feature");
            });

            t.Cell().Text("Docotic.Pdf.Layout add-on");
            t.Cell().Text("Generate PDF");
            t.Cell().Text("Docotic.Pdf.HtmlToPdf add-on");
            t.Cell().Text("HTML to PDF");
        });

        page.Footer().AlignCenter().Text(t => t.CurrentPageNumber());
    }));