Pdfium.Net.Free 一个免费的Pdfium的 .net包装器--删除或编辑pdf内容

项目地址：

Pdfium.Net：https://github.com/1000374/Pdfium.Net

PdfiumViewer：https://github.com/1000374/PdfiumViewer

如需删除或者编辑pdf中的内容，首先要获取pdf内需要修改或者删除的对象，所有对页面编辑操作都需要调用GenerateContent函数方才生效

获取pdf所有对象的方法：

返回的信息包含当前对象的index、文字及字体信息（如对象是文本）、位置信息

 var pathPdf = "./Pdfium.NetTests/resources/fontText.pdf";
 using (var doc = PdfDocument.Load(new MemoryStream(File.ReadAllBytes(pathPdf))))
 {
     var page0 = doc.Pages[0];
     var infos = page0.GetCharacterInformation();
 }

如上述不能满足需求，请使用下示例获取：

  //How to know "GetObject" index?
  var pathPdf = "./Pdfium.NetTests/resources/fontText.pdf";
  using (var doc = PdfDocument.Load(new MemoryStream(File.ReadAllBytes(pathPdf))))
  {
      var arr = "武则天".ToCharArray();
      var page0 = doc.Pages[0];
      var count = page0.GetObjectsCount();
      for (int i = 0; i < count; i++)
      {
          var obj = page0.GetObject(0);
          if (!obj.IsNull)
          {
              var objType = obj.PageObjGetObjType();
              switch (objType)
              {
                  case FpdfPageObj.FPDF_PAGEOBJ_UNKNOWN:
                      {

                      }
                      break;
                  case FpdfPageObj.FPDF_PAGEOBJ_TEXT:
                      {
                          var txt = obj.TextObjGetText(page0.PageText);
                      }
                      break;
                  case FpdfPageObj.FPDF_PAGEOBJ_PATH:
                      {
                          var res = obj.PathMoveTo(10, 20);
                      }
                      break;
                  case FpdfPageObj.FPDF_PAGEOBJ_IMAGE:
                      {
                          /* Matrix: | a, c, e| ==> | width, 0,      offsetX|
                           *         | b, d, f|     | 0,     height, offsetY|*/
                          var bitmap = obj.ImageObjGetBitmap();
                          var res = obj.ImageObjSetMatrix(bitmap.Width, 0.1, 0, bitmap.Height, 100, 100);
                          if (!bitmap.IsNull)
                          {
                              //There is a feature request discussing this: https://crbug.com/pdfium/1930 (disclaimer: I'm the reporter)
                              //TLDR The functions you mention do provide the main data stream, but for some filters complementary data would be needed to actually re - construct the image, which pdfium does not provide.

                              //For CCITTDecode, as the TIFF format can use, pdfium's public API does not tell the CCITT group, but this would be needed to re-construct the TIFF header, which the PDF format strips. And I think BlackIs1 info would also be needed; possibly more.
                              //JBIG2Decode may optionally use a separate JBIG2Globals stream, which again pdfium does not provide.I had filed a separate bug about this: https://crbug.com/pdfium/1927. However, I guess the raw JBIG2 data might not be very useful except for re-insertion into a PDF. IIRC the way pikepdf handles JBIG2 extraction to files is to just decode the data and re-encode to some other format. From a programmatic POV that's not ideal, but I guess the context is that standalone JBIG2 isn't really supported by end-user apps.
                              //Concerning FPDFImageObj_GetImageDataDecoded(), note that it does not fully decode images; it only applies "simple" filters(see https://crbug.com/pdfium/1203#c7), so the function name is a bit misleading.

                              //For the plain pixel data, you can use FPDFImageObj_GetBitmap(), FPDFBitmap_GetBuffer() & co, but note that FPDF_BITMAP is limited in supported pixel formats and bit depth(e.g.no CMYK, B / W, > 8bpc RGB(A), ...).
                          }
                      }
                      break;
                  case FpdfPageObj.FPDF_PAGEOBJ_SHADING:
                      {

                      }
                      break;
                  case FpdfPageObj.FPDF_PAGEOBJ_FORM:
                      {

                      }
                      break;
              }
          }
      }
      page0.GenerateContent();
  }

编辑对象代码示例（文本）：经测试、对于中文替换有时会出现乱码，暂未发现设置字库的方式，可通过先删除在添加文本的方式修改

  var pathPdf = "./Pdfium.NetTests/resources/hello_world.pdf";
  using (var doc = PdfDocument.Load(new MemoryStream(File.ReadAllBytes(pathPdf))))
  {
      //var fontPath = @"c:\Windows\fonts\simhei.ttf";
      //doc.LoadFont(fontPath);
      var page0 = doc.Pages[0];
      var obj = page0.GetObject(0);
      if (!obj.IsNull)
      {
          if (!obj.IsNull)
          {
              var objType = obj.PageObjGetObjType();
              switch (objType)
              {
                  case FpdfPageObj.FPDF_PAGEOBJ_TEXT:
                      {
                          var txt = obj.TextObjGetText(page0.PageText);
                          var res = obj.TextSetText("Changed for SetText test");
                      }
                      break;
              }
          }
          page0.GenerateContent();
          doc.Save("./Pdfium.NetTests/TextObjFontChange.pdf");
      }
  }

删除对象：

  var pathPdf = "./Pdfium.NetTests/resources/fontText.pdf";
  using (var doc = PdfDocument.Load(new MemoryStream(File.ReadAllBytes(pathPdf))))
  {
      var page0 = doc.Pages[0];
      var obj = page0.GetObject(0);
      if (!obj.IsNull)
      {
          var res = page0.RemoveObject(obj);
          page0.GenerateContent();
          doc.Save("./Pdfium.NetTests/TextObjFont.pdf");
      }
  }