项目地址：
Pdfium.Net：https://github.com/1000374/Pdfium.Net
PdfiumViewer：https://github.com/1000374/PdfiumViewer
Pdfium.Net 添加文本有3个重载
1.当前重载使用pdf标准字库添加文字（中文会乱码）
/// <summary>
/// Add text object using one of the standard PDF fonts. Chinese maybe garbled characters
/// </summary>
/// <param name="text"></param>
/// <param name="posX"></param>
/// <param name="posY"></param>
/// <param name="font_size">the font size for the new text object.</param>
/// <param name="fillColor"></param>
/// <param name="fontName"><see cref="Native.Enums.StandardPDFFonts"/></param>
/// <param name="scalex"></param>
/// <param name="scaley"></param>
/// <param name="rotate"></param>
/// <param name="shear"></param>
/// <param name="blend">Blend mode can be one of following: Color, ColorBurn, ColorDodge, Darken,Difference, Exclusion, HardLight, Hue, Lighten, Luminosity, Multiply, Normal,Overlay, Saturation, Screen, SoftLight.<see cref="BlendMode"/></param>
/// <param name="render_mode">render_mode<see cref="FpdfTextRenderMode"/></param>
/// <param name="strokeColor">stroke Color render_mode </param>
/// <param name="strokeWidth">stroke Width</param>
/// <returns></returns>
public bool AddString(string text, int posX, int posY, float font_size, Color fillColor, string fontName, float scalex = 1f, float scaley = 1, float rotate = 0, float shear = 0,
string blend = BlendMode.Darken, FpdfTextRenderMode render_mode = FpdfTextRenderMode.FILL, Color? strokeColor = null, float strokeWidth = 0.2f)
调用示例：
using (var doc = PdfDocument.CreateNew())
{
var cSharpString = "!you ok 这是第一句。 这是第二行。a you ok";
var page = doc.Pages.Add(612, 792);
page.AddString(cSharpString, 10, 50, 12, Color.Black, StandardPDFFonts.TimesNewRoman);
doc.Save("./Pdfium.NetTests/AddString1.pdf");
}
2.当前重载使用获取的PdfFont 对象添加文字，详情请参照
Pdfium.Net.Free 一个免费的Pdfium的 .net包装器--加载字体 
/// <summary> /// add Text with add <see cref="FpdfFontT"/> /// </summary> /// <param name="pageNumber"></param> /// <param name="text"></param> /// <param name="posX"></param> /// <param name="posY"></param> /// <param name="font_size"></param> /// <param name="fillColor"></param> /// <param name="font"></param> /// <param name="scalex"></param> /// <param name="scaley"></param> /// <param name="rotate"></param> /// <param name="shear"></param> /// <param name="blend">Blend mode can be one of following: Color, ColorBurn, ColorDodge, Darken,Difference, Exclusion, HardLight, Hue, Lighten, Luminosity, Multiply, Normal,Overlay, Saturation, Screen, SoftLight.<see cref="BlendMode"/></param> /// <param name="render_mode">render_mode<see cref="FpdfTextRenderMode"/></param> /// <param name="strokeColor">stroke Color render_mode </param> /// <param name="strokeWidth">stroke Width</param> /// <returns></returns> public bool AddString(string text, float posX, float posY, float font_size, Color fillColor, PdfFont font, float scalex = 1f, float scaley = 1, float rotate = 0, float shear = 0, string blend = BlendMode.Darken, FpdfTextRenderMode render_mode = FpdfTextRenderMode.FILL, Color? strokeColor = null, float strokeWidth = 0.2f)
调用示例（从pdf中获取字体后写入）：
var pathPdf = "./Pdfium.NetTests/resources/fontText.pdf";
using (var doc = PdfDocument.Load(new MemoryStream(File.ReadAllBytes(pathPdf))))
{
var font = doc.Pages[0].GetTextObjFont("你", out float size);
if (!font.IsNull)
{
var emb = font.IsEmbedded;
var cSharpString = "你好啊,abc";
var page = doc.Pages[0];
page.AddString(cSharpString, 10, 50, size, Color.Black, font);
doc.Save("./Pdfium.NetTests/TextObjFont.pdf");
}
}
3.当前重载需提前调用
public void LoadFont(string fontPath, bool isSubSet = false, string words = null, FpdfFontTypes fontTypes = FpdfFontTypes.TrueType)
方法，且只能调用一次，否则抛出找不到字体对象，或者pdf会多次加载字体导致pdf很大，也就是每次调用都会往doc中加载一次字库。
可创建子集后加载字库，以减少pdf大小，具体参照
Pdfium.Net.Free 一个免费的Pdfium的 .net包装器--创建字符子集
/// <summary> /// add Text with add <see cref="FpdfFontT"/> /// </summary> /// <param name="text"></param> /// <param name="posX"></param> /// <param name="posY"></param> /// <param name="font_size">the font size for the new text object.</param> /// <param name="fillColor">the font color.</param> /// <param name="isSubSet">ttf path use File.ReadAllBytes(fontPath);</param> /// <param name="scalex">scale x</param> /// <param name="scaley">scale y</param> /// <param name="rotate">rotate</param> /// <param name="shear">shear</param> /// <param name="fontTypes"><see cref="FpdfFontTypes"/></param> /// <param name="blend">Blend mode can be one of following: Color, ColorBurn, ColorDodge, Darken,Difference, Exclusion, HardLight, Hue, Lighten, Luminosity, Multiply, Normal,Overlay, Saturation, Screen, SoftLight.<see cref="BlendMode"/></param> /// <param name="render_mode">render_mode<see cref="FpdfTextRenderMode"/></param> /// <param name="strokeColor">stroke Color render_mode </param> /// <param name="strokeWidth">stroke Width</param> /// <returns></returns> public bool AddString(string text, float posX, float posY, float font_size, Color fillColor, float scalex = 1f, float scaley = 1, float rotate = 0, float shear = 0, FpdfFontTypes fontTypes = FpdfFontTypes.TrueType, string blend = BlendMode.Darken, FpdfTextRenderMode render_mode = FpdfTextRenderMode.FILL, Color? strokeColor = null, float strokeWidth = 0.2f)
调用字符集全部加载示例：
using (var doc = PdfDocument.CreateNew())
{
var fontPath = @"c:\Windows\fonts\simhei.ttf";
doc.LoadFont(fontPath);
var cSharpString = "!you ok 这是第一句。 这是第二行。a you ok";
var page = doc.Pages.Add(612, 792);
page.AddString(cSharpString, 10, 50, 12, Color.Black);
doc.Save("./Pdfium.NetTests/AddString.pdf");
}
创建字符子集加载示例：
using (var doc = PdfDocument.CreateNew())
{
var fontPath = @"c:\Windows\fonts\simhei.ttf";
var cSharpString = "!you ok 这是第一句。";
var cSharpString2 = " 这是第二行。a you ok 你好 abcdefghijklmnopqrstuvwxyz1234567890-*/+~`@#$%^&*(){}[];:'|?,，。.！!";
doc.LoadFont(fontPath, true, cSharpString + cSharpString2);
var page = doc.Pages.Add(612, 792);
page.AddString(cSharpString, 10, 50, 12, Color.Black);
page.AddString(cSharpString2, 10, 80, 12, Color.Black);
doc.Save("./Pdfium.NetTests/AddString3.pdf");
}
标签：Pdfium,--,doc,float,Free,Color,mode,var From： https://www.cnblogs.com/xiaohemiao/p/17995042