merging byte array of pdf

[sand will]

I am receiving 2 byte array of pdf. I want to merge these to bye array in to single byte array so that I can display single pdf.
I have written below code but I give error message that "The File is damaged and could not be repaired"
I tried with one byte array at a time and it does generate pdf properly.
What is wrong if I combine byte arrays.

byte[] pdfBytes1 = eFormsService.renderNewEForm("t01b3l7", formSpecId, getBaseUrl(request), getLoggedInUser());
byte[] pdfBytes2 = eFormsService.renderNewEForm("t01b3l7", 17, getBaseUrl(request), getLoggedInUser());
byte[] combined = new byte[pdfBytes1.length + pdfBytes2.length];
System.arraycopy(pdfBytes1,0,combined,0 ,pdfBytes1.length);
System.arraycopy(pdfBytes2,0,combined,pdfBytes1.length,pdfBytes2.length);

response.setContentType("application/pdf");
response.setContentLength(combined.length);

response.setHeader("Content-disposition", "inline; filename=" + formSpecId + ".pdf");
response.setHeader("Expires", "0");
response.setHeader("Cache-Control", "must-revalidate, no-store, post-check=0, pre-check=0");
//response.getOutputStream().write(pdfBytes1);
response.getOutputStream().write(combined);

[Ulf Dittmer]

You can't simply append structured document formats in the way you would do with text files. But there's no shortage of libraries that will merge PDF documents for you; check out Apache PDFBox.

[sand will]

Thank you for your reply "Ulf Dittmer". Actually client has asked us not to use any third party tool or API.So I was wondering if there is a way to play with byte array to merge the pdf documents.

[Ulf Dittmer]

There isn't. PDF is a very complex format, without a library that knows the format very well you'll get nowhere.