doc.Info.Title = "Archival Document";
doc.Info.Author = "ObviousPDF";
doc.Language = "en-US";
doc.DisplayDocTitle = true;

// Declare PDF/A-2b conformance
// Automatically adds: XMP metadata,
// OutputIntent, sRGB ICC profile
doc.PdfAConformance =
    PdfAConformanceLevel.PdfA2B;

// Build tagged content as usual...
var root = doc.EnableTaggedPdf();
var h1 = root.AddChild(StructureType.H1);
page.AddTaggedText(h1,
    "PDF/A Archival Document", 72, 740);

doc.Save("archival.pdf");