Nice and simple to combine multiple pdf’s into one pdf file.

  1. sudo apt-get install gs pdftk
  2. gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=NameOfTheCombinedPDF.pdf
    -dBATCH 1.pdf 2.pdf 3.pdf

Works like a charm!