OK, if you mean the Page Content Stream the codes like:
        PageContent content = new PageContent();
	content.Create();//create content, do not forget.
		//prepare to write texts
		content.GSSave();
		mat = new Matrix( 1, 1, 80, 200 );
		content.GSSetMatrix(mat);
		mat.Destroy();
        //the font name must exists on font list, that initialized in Global.Init();
	DocFont dfont = m_doc.NewFontCID("DroidSansFallback", 3 | 8);//bold-italic and embed in horizontal writing
        if(dfont == null)
        {
            dfont = m_doc.NewFontCID("Roboto-Regular", 3 | 8);
            if(dfont == null)
                dfont = m_doc.NewFontCID("DroidSans", 3 | 8);
        }
		ResFont rfont = page.AddResFont(dfont);
		content.TextBegin();
		content.TextSetFont(rfont, 16);//set font and size
		content.SetFillColor(0x8000);//set fill color to black-green.
		content.SetStrokeColor(0x80);//set stroke color to black-red.
		content.TextSetCharSpace(0);
		content.TextSetWordSpace(0.2f);
		content.TextSetLeading(16);
		content.TextSetRenderMode(2);//fill and stroke
		content.TextSetHScale(120);//set horizontal scale
		content.DrawText("Hello word!\rNice to meet you!");
		content.TextEnd();
		content.GSRestore();
		page.AddContent(content, true);
		content.Destroy();
		page.Close();if you mean annotation, you can using Page.AddAnnotEditbox() to add an editbox on page,
and then using Annotation.SetEditText() to set text value.