Using itextsharp (or any c# pdf library), how to open a PDF, replace some text, and save it again?

Question

Using itextsharp (or any c# pdf library), i need to open a PDF, replace some placeholder text with actual values, and return it as a byte[].

Can someone suggest how to d

Answer 1

Unfortunately I was looking for something similar and could not figure it out. Below was about as far as I got, maybe you can use this as a starting point. The problem is that PDF does not actually save text, but instead uses lookup tables and some other arcane wizardry. This method reads the byte-values for the page and attempts to convert to string, but as far as I can tell it can only do English and misses on some special characters, so I gave up my project and moved on.

string contents = string.Empty();
Document doc = new Document();
PdfReader reader = new PdfReader("pathToPdf.pdf");
using (MemoryStream memoryStream = new MemoryStream())
{

    PdfWriter writer = PdfWriter.GetInstance(doc, memoryStream);
    doc.Open();
    PdfContentByte cb = writer.DirectContent;
    for (int p = 1; p <= reader.NumberOfPages; p++)
    {
        // add page from reader
        doc.SetPageSize(reader.GetPageSize(p));
        doc.NewPage();

        // pickup here something like this:
        byte[] bt = reader.GetPageContent(p);
        contents = ExtractTextFromPDFBytes(bt);

        if (contents.IndexOf("something")!=-1)
        {
            // make your own pdf page and add to cb (contentbyte)

        }
        else
        {
            PdfImportedPage page = writer.GetImportedPage(reader, p);
            int rot = reader.GetPageRotation(p);
            if (rot == 90 || rot == 270)
                cb.AddTemplate(page, 0, -1.0F, 1.0F, 0, 0, reader.GetPageSizeWithRotation(p).Height);
            else
                cb.AddTemplate(page, 1.0F, 0, 0, 1.0F, 0, 0);
        }
    }
    reader.Close();
    doc.Close();
    File.WriteAllBytes("pathToOutputOrSamePathToOverwrite.pdf", memoryStream.ToArray());

This is taken from this site.

private string ExtractTextFromPDFBytes(byte[] input) 
{ 
    if (input == null || input.Length == 0) return ""; 

     try 
     { 
         string resultString = ""; 

         // Flag showing if we are we currently inside a text object 
         bool inTextObject = false; 

         // Flag showing if the next character is literal  
         // e.g. '\\' to get a '\' character or '\(' to get '(' 
         bool nextLiteral = false; 

         // () Bracket nesting level. Text appears inside () 
         int bracketDepth = 0; 

         // Keep previous chars to get extract numbers etc.: 
         char[] previousCharacters = new char[_numberOfCharsToKeep]; 
         for (int j = 0; j < _numberOfCharsToKeep; j++) previousCharacters[j] = ' '; 


          for (int i = 0; i < input.Length; i++) 
          { 
              char c = (char)input[i]; 

              if (inTextObject) 
              { 
                  // Position the text 
                  if (bracketDepth == 0) 
                  { 
                      if (CheckToken(new string[] { "TD", "Td" }, previousCharacters)) 
                      { 
                          resultString += "\n\r"; 
                      } 
                      else 
                      { 
                          if (CheckToken(new string[] { "'", "T*", "\"" }, previousCharacters)) 
                          { 
                               resultString += "\n"; 
                           } 
                           else 
                           { 
                               if (CheckToken(new string[] { "Tj" }, previousCharacters)) 
                                { 
                                    resultString += " "; 
                                } 
                            } 
                        } 
                    }

                    // End of a text object, also go to a new line. 
                    if (bracketDepth == 0 && 
                        CheckToken(new string[] { "ET" }, previousCharacters)) 
                    { 

                        inTextObject = false; 
                        resultString += " "; 
                   } 
                   else 
                   { 
                        // Start outputting text 
                        if ((c == '(') && (bracketDepth == 0) && (!nextLiteral)) 
                        { 
                            bracketDepth = 1; 
                        } 
                        else 
                        { 
                            // Stop outputting text 
                            if ((c == ')') && (bracketDepth == 1) && (!nextLiteral)) 
                            { 
                                 bracketDepth = 0; 
                            } 
                            else 
                            { 
                                // Just a normal text character: 
                                if (bracketDepth == 1) 
                                { 
                                    // Only print out next character no matter what.  
                                    // Do not interpret. 
                                    if (c == '\\' && !nextLiteral) 
                                    { 
                                        nextLiteral = true; 
                                    } 
                                    else 
                                    { 
                                        if (((c >= ' ') && (c <= '~')) || 
                                            ((c >= 128) && (c < 255))) 
                                        { 
                                            resultString += c.ToString(); 
                                        } 

                                        nextLiteral = false; 
                                    } 
                                } 
                            } 
                        } 
                    } 
                } 

                // Store the recent characters for  
                // when we have to go back for a checking 
                for (int j = 0; j < _numberOfCharsToKeep - 1; j++) 
                { 
                    previousCharacters[j] = previousCharacters[j + 1]; 
                } 
                previousCharacters[_numberOfCharsToKeep - 1] = c; 

                // Start of a text object 
                if (!inTextObject && CheckToken(new string[] { "BT" }, previousCharacters)) 
                { 
                    inTextObject = true; 
                } 
            } 
        return resultString; 
    } 
    catch 
    { 
        return ""; 
     } 
} 

 private bool CheckToken(string[] tokens, char[] recent) 
 { 
     foreach (string token in tokens) 
     { 
         if ((recent[_numberOfCharsToKeep - 3] == token[0]) && 
           (recent[_numberOfCharsToKeep - 2] == token[1]) && 
           ((recent[_numberOfCharsToKeep - 1] == ' ') || 
           (recent[_numberOfCharsToKeep - 1] == 0x0d) || 
           (recent[_numberOfCharsToKeep - 1] == 0x0a)) && 
           ((recent[_numberOfCharsToKeep - 4] == ' ') || 
           (recent[_numberOfCharsToKeep - 4] == 0x0d) || 
           (recent[_numberOfCharsToKeep - 4] == 0x0a))) 
           { 
               return true; 
           } 
    }
    return false; 
}