if (annotation is PdfLineAnnotationWidget)
{
    PdfLineAnnotationWidget lineAnn = annotation as PdfLineAnnotationWidget;
    //PdfLineAnnotation lineAnn = annotation as PdfLineAnnotation;
    lineAnn.Author = "Author_test";
    lineAnn.Subject = "Subject_test";
}

checkboxField.ForeColor = new PdfRGBColor(Color.Red);

PdfStringFormat format = new PdfStringFormat();
PdfTrueTypeFont font = new PdfTrueTypeFont(new System.Drawing.Font("Times New Roman", 10));
PdfPen pen = PdfPens.Black;
PdfSolidBrush brush = new PdfSolidBrush(Color.Black);

PdfDocument doc = new PdfDocument("HelloWord.pdf");
PdfLogicalStructure tree = PdfLogicalStructure.CreateLogicalStructure(doc);
PdfStructureElement article = tree.AppendChildElement(PdfStandardStructTypes.Article);
article.Title = "create tagged pdf";

PdfStructureElement paragraph1 = article.AppendChildElement(PdfStandardStructTypes.Paragraph);
paragraph1.Title = "text paragraph1";
int mcid = 0;
paragraph1.BeginMarkedContentSequence(doc.Pages[0].Canvas, "paragraph1", mcid);

doc.Pages[0].Canvas.DrawString("paragraph1: PDF’s logical structure facilities (PDF 1.3) provide a mechanism for " 
+ "incorporating structural information about a document’s content into a PDF file. Such information might include," 
+ "for example, the organization of the document into chapters and sections or the identification of special elements" 
+ "such as figures, tables, and footnotes. The logical structure facilities are extensible, allowing applications that" 
+ "produce PDF files to choose what structural information to include and how to represent it, while enabling PDF" 
+ "consumers to navigate a file without knowing the producer’s structural conventions.", 
font, pen, brush, new Rectangle(40, 200, 480, 80), format);
paragraph1.EndMarkedContentSequence(doc.Pages[0].Canvas);
paragraph1.ReferenceContent(doc.Pages[0], mcid);

PdfStructureElement paragraph2 = article.AppendChildElement(PdfStandardStructTypes.Paragraph);
paragraph2.Title = "text paragraph2";
mcid = 1;
paragraph2.BeginMarkedContentSequence(doc.Pages[0].Canvas, "paragraph2", mcid);
doc.Pages[0].Canvas.DrawString("paragraph2: PDF logical structure shares basic features with standard document markup languages" 
+ "such as HTML, SGML, and XML. A document’s logical structure is expressed as a hierarchy of structure elements, each" 
+ "represented by a dictionary object. Like their counterparts in other markup languages, PDF structure elements can" 
+ "have content and attributes. In PDF, rendered document content takes over the role occupied by text in HTML, SGML, and XML.", 
font, pen, brush, new Rectangle(40, 280, 480, 60), format);
paragraph2.EndMarkedContentSequence(doc.Pages[0].Canvas);
paragraph2.ReferenceContent(doc.Pages[0], mcid);

doc.SaveToFile("Tagged.pdf");