static void Main(string[] args)
{
	PdfCommon.Initialize();

	//Save text to existing document
	var doc = PdfDocument.Load(@"d:\1\review.pdf");
	var pageDict = doc.Pages[0].Dictionary;
	AddTextToPage(doc, doc.Pages[0]);

	//or to newly created document
	var doc = PdfDocument.CreateNew();
	doc.Pages.InsertPageAt(0, 500, 500);
	AddTextToPage(doc, doc.Pages[0]);
}

private static void AddTextToPage(PdfDocument doc, PdfPage page)
{
	var pageDict = page.Dictionary;


	//Create and insert a text object
	PdfTextObject txtObj = PdfTextObject.Create();
	LOGFONT lf = new LOGFONT() { lfCharSet = LOGFONT.FontCharSet.ANSI_CHARSET, lfPitchAndFamily = LOGFONT.FontPitchAndFamily.DEFAULT_PITCH | LOGFONT.FontPitchAndFamily.FF_ROMAN, lfWeight = LOGFONT.FontWeight.FW_BOLD };
	txtObj.Font = PdfFont.CreateWindowsFont(doc, lf, false, true);
	txtObj.FillColor = Color.Blue;
	txtObj.Transform(50, 0, 0, 50, 0, 0);
	txtObj.Location = new PointF(50, 50);
	txtObj.TextUnicode = "Hello World";
	page.PageObjects.InsertObject(txtObj);


	//Get the list of indirect objects and add the text object Font dictionary into it
	var list = PdfIndirectList.FromPdfDocument(doc);
	int objNum = list.Add(txtObj.Font.Dictionary);
	//Create an indirect object for text object Font dictionary
	var indirect = PdfTypeIndirect.Create(list, objNum);

	//Get "Font" dictionary from page resource
	PdfTypeDictionary fontDict = GetFontDictFromResource(pageDict, list);

	//Insert that indirect object into Page's resources
	fontDict.Add("FontMyQniqName", indirect);

	//Create streram for the text object 
	var stream = PdfTypeStream.Create();
	objNum = list.Add(stream);
	indirect = PdfTypeIndirect.Create(list, objNum);

	//Encode text object and insert it into stream
	byte[] data = EncodeTextObject(txtObj);
	var streamDict = PdfTypeDictionary.Create();
	streamDict.Add("Length", PdfTypeNumber.Create(data.Length));
	stream.Init(data, streamDict);

	//Get page's content and add text stream into it
	PdfTypeArray contents = GetContentsAsArray(list, pageDict);
	contents.Add(indirect, list);

	//Save document
	doc.Save(@"d:\1\review_modified.pdf", SaveFlags.NoIncremental);
}

private static PdfTypeDictionary GetFontDictFromResource(PdfTypeDictionary pageDict, PdfIndirectList list)
{
	var res = (pageDict["Resources"] as PdfTypeDictionary);
	if (!res.ContainsKey("Font"))
	{
		var ret = PdfTypeDictionary.Create();
		int objNum = list.Add(ret);
		var indirect = PdfTypeIndirect.Create(list, objNum);
		res.Add("Font", indirect);
		return ret;
	}
	var font = res["Font"];
	if (font is PdfTypeDictionary)
		return font as PdfTypeDictionary;
	else if(font is PdfTypeIndirect)
	{
		if ((font as PdfTypeIndirect).Direct is PdfTypeDictionary)
			return (font as PdfTypeIndirect).Direct as PdfTypeDictionary;
	}

	throw new Exception("Unexpected type of font resource");
}

public static PdfTypeArray GetContentsAsArray(PdfIndirectList list, PdfTypeDictionary pageDict)
{
	if(!pageDict.ContainsKey("Contents"))
	{
		var array = PdfTypeArray.Create();
		//Add array into list of indirect objects
		list.Add(array);
		//And set it as a contents of the page
		pageDict.SetIndirectAt("Contents", list, array);
		return array;
	}

	var contents = pageDict["Contents"];

	//check the original content whether it's an array
	if (contents is PdfTypeArray)
		return contents as PdfTypeArray;  //if contents is a array just return it
	else if (contents is PdfTypeIndirect)
	{
		if ((contents as PdfTypeIndirect).Direct is PdfTypeArray)
			return (contents as PdfTypeIndirect).Direct as PdfTypeArray; //if contents is a reference to array then return that array
		else if ((contents as PdfTypeIndirect).Direct is PdfTypeStream)
		{
			//if contents is a reference to a stream then create a new array and insert stream as a first element of array
			var array = PdfTypeArray.Create();
			array.AddIndirect(list, (contents as PdfTypeIndirect).Direct);
			//Add array into list of indirect objects
			list.Add(array);
			//And set it as a contents of the page
			pageDict.SetIndirectAt("Contents", list, array);
			return array;
		}
		else
			throw new Exception("Unexpected content type");
	}
	else
		throw new Exception("Unexpected content type");
}

private static byte[] EncodeTextObject(PdfTextObject txtObj)
{
	string ret = string.Format(
		@"BT
/FontMyQniqName {0} Tf
{1} {2} {3} {4} {5} {6} Tm
{7} {8} {9} rg
({10})Tj
ET",
		txtObj.FontSize,
		txtObj.Matrix.a, txtObj.Matrix.b, txtObj.Matrix.c, txtObj.Matrix.d, txtObj.Matrix.e, txtObj.Matrix.f,
		txtObj.FillColor.R, txtObj.FillColor.G, txtObj.FillColor.B,
		txtObj.TextAnsi
		);
	return System.Text.Encoding.GetEncoding(1251).GetBytes(ret);
}