Quickly concatenating PDF files with teTeX utilities
To concatenate 1.pdf, 2.pdf, 3.pdf into a single file 123.pdf you can use the command
texexec --pdfarrange --result 123.pdf 1.pdf 2.pdf 3.pdf
To concatenate all pdf files in a directory into a single file all.pdf you can use
texexec --pdfarrange --result all.pdf *.pdf