How to concatenate several PDF files

Use Ghostscript. There is no Mac package, but a ./configure --without-x && make && sudo make install will do. Ghostscript offers a wealth of functions to generate or manipulate existing PDFs, check http://pages.cs.wisc.edu/~ghost/doc/cvs/Use.htm#Options for details.
So, to concatenate: gs -q -sPAPERSIZE=a4 -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=out.pdf in1.pdf in2.pdf ...

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