PyPdf: How to Write a PDF to Memory http://www.blog.pythonlibrary.org/2013/07/16/pypdf-how-to-write-a-pdf-to-memory/

demo.py

import pyPdf
from StringIO import StringIO
 
#----------------------------------------------------------------------
def mergePDFs(pdfOne, pdfTwo):
    """
    Merge PDFs
    """
    tmp = StringIO()
 
    output = pyPdf.PdfFileWriter()
 
    pdfOne = pyPdf.PdfFileReader(file(pdfOne, "rb"))
    for page in range(pdfOne.getNumPages()):
        output.addPage(pdfOne.getPage(page))
    pdfTwo = pyPdf.PdfFileReader(file(pdfTwo, "rb"))
    for page in range(pdfTwo.getNumPages()):
        output.addPage(pdfTwo.getPage(page))
 
    output.write(tmp)
    return tmp.getvalue()
 
 
if __name__ == "__main__":
    pdfOne = '/path/to/pdf/one'
    pdfTwo = '/path/to/pdf/two'
    pdfObj = mergePDFs(pdfOne, pdfTwo)