# Concatenate all pdf files into one:
pdftk *.pdf cat output all.pdf
# Concatenate specific pdf files into one:
pdftk 1.pdf 2.pdf 3.pdf cat output 123.pdf
# Concatenate pages 1 to 5 of first.pdf with page 3 of second.pdf
pdftk A=fist.pdf B=second.pdf cat A1-5 B3 output new.pdf
