[[https://www.fosslinux.com/49661/merge-pdf-files-on-linux.htm#:~:text=Combine%20PDFs%20with%20the%20gs%20command&text=Use%20the%20%2DsDEVICE%20attribute%20to,command%20above%20will%20output%20merged_file|Merge PDF files]]

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



[[http://www.linux.com/news/software/applications/8229-putting-together-pdf-files]]

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

CentOS6: Install pdfjam and use pdfjoin