How to combine several pdf files into one single pdf file

In Linux, we can use the following command to merge several pdf files into a single pdf file:

gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=combinedpdf.pdf -dBATCH *.pdf

Another way is to use the handy tool called "pdftk":

pdftk *.pdf cat output combinedpdf.pdf