we will see one example how to combine pdf files let us assume we have 001.pdf, 002.pdf files and now we need to combine this files using the following command
gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=combinedpdf.pdf -dBATCH 001.pdf 002.pdf
gswin32c.exe -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=combinedpdf.pdf -dBATCH 001.pdf 002.pdf
In the above command after “-sOUTPUTFILE=” type whatever name you want for the merged file (don’t forget to append .pdf to the end of the file name).
After you run the above command, a new PDF file called combinedpdf.pdf will be created with your individual files merged according to the order you list.
Reference:
http://www.debianadmin.com/combine-multiple-pdfs-into-one-file-in-ubuntu-linux.html
http://www.rizauddin.com/2009/04/how-to-merge-or-combine-pdf-files-with-ghostscript