This command makes possible to join several PDF files into a single one using Ghostscript. Try to do the following in the command line:

gs -dBATCH -q -sDEVICE=pdfwrite -sOutputFile=outputfile.pdf inputfile-1.pdf inputfile-2.pdf (...) inputfile-n.pdf 

It has also the advantage to reduce size of the resulting PDF, even if you use only one input file.