Merge 2 pdf byte streams using Itextsharp

Question

I have a method that returns a pdf byte stream (from fillable pdf) Is there a straight forward way to merge 2 streams into one stream and make one pdf out of it? I need to run my method twice but need the two pdf's into One pdf stream. Thanks.

Are the byte streams made by iTextSharp? Are the separate byte streams from two different fillable forms, or a single form? If they're coming from a single form, did you flatten them? — kuujinbo, Dec 24 '11 at 12:20
Forget about byte streams for a moment. Is your question really "how do I combine two PDFs into one?" — Chris Haas, Dec 24 '11 at 14:43
It's the same fillable PDF. I used Itexsharp pdf stamper. Right now using it in asp.net and streaming this pdf to the browser. So, my need is to also call my method that streams the same pdf but giving different data and put eevrything in one stream. So, the same PDF would appear twice as a single PDF. — user282807, Dec 25 '11 at 00:14
@Chris, yes my question is how to take two pdf byte streams and return one PDF byte stream. — user282807, Dec 25 '11 at 00:17

score 3 · Accepted Answer · edited May 23 '17 at 11:55

You didn't say if you're flattening the filled forms with the PdfStamper, so I'll just say you must flatten the before trying to merge them. Here's a working .ashx HTTP handler:

<%@ WebHandler Language="C#" Class="mergeByteForms" %>
using System;
using System.IO;
using System.Web;
using iTextSharp.text;
using iTextSharp.text.pdf;

public class mergeByteForms : IHttpHandler {
  HttpServerUtility Server;
  public void ProcessRequest (HttpContext context) {
    Server = context.Server;
    HttpResponse Response = context.Response;
    Response.ContentType = "application/pdf";
    using (Document document = new Document()) {
      using (PdfSmartCopy copy = new PdfSmartCopy(
        document, Response.OutputStream) ) 
      {
        document.Open();
        for (int i = 0; i < 2; ++i) {
          PdfReader reader = new PdfReader(_getPdfBtyeStream(i.ToString()));
          copy.AddPage(copy.GetImportedPage(reader, 1));
        }
      }
    }
  }
  public bool IsReusable { get { return false; } }

// simulate your method to use __one__ byte stream for __one__ PDF  
  private byte[] _getPdfBtyeStream(string data) {
// replace with __your__ PDF template
    string pdfTemplatePath = Server.MapPath(
      "~/app_data/template.pdf"
    );
    PdfReader reader = new PdfReader(pdfTemplatePath);
    using (MemoryStream ms = new MemoryStream()) {
      using (PdfStamper stamper = new PdfStamper(reader, ms)) {
        AcroFields form = stamper.AcroFields;
// replace this with your form field data
        form.SetField("title", data);
        // ...
// this is __VERY__ important; since you're using the same fillable
// PDF, if you don't set this property to true the second page will
// lose the filled fields.          
        stamper.FormFlattening = true;
      }
      return ms.ToArray();
    }
  }
}

Hopefully the inline comments make sense. _getPdfBtyeStream() method above simulates your PDF byte streams. The reason you need to set FormFlattening to true is that a when you fill PDF form fields, names are supposed to be unique. In your case the second page is the same fillable PDF form, so it has the same field names as the first page and when you fill them they're ignored. Comment out the example line above:

stamper.FormFlattening = true;

to see what I mean.

In other words, a lot of the generic code to merge PDFs on the Internet and even here on stackoverflow will not work (for fillable forms) because Acrofields are not being accounted for. In fact, if you take a look at stackoverflow's about itextsharp tag "SO FAQ & Popular" to Merge PDFs, it's mentioned in the third comment for the correctly marked answer by @Ray Cheng.

Another way to merge fillable PDF (without flattening the form) is to rename the form fields for the second/following page(s), but that's more work.

Thanks Kuujinbo for the answer and explanation. – user282807 Dec 28 '11 at 04:33 — user282807, Dec 28 '11 at 04:33

Merge 2 pdf byte streams using Itextsharp

1 Answers1