Merge PDF files

$ gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=merged_file.pdf -dBATCH pdf_1.pdf pdf_2.pdf

$ gs -dBATCH -dNOPAUSE -q -sDEVICE=pdfwrite -sOutputFile=OUTFILE.pdf file1.pdf file2.pdf