There is package poppler-utils available on Debian and Ubuntu.
apt-get install poppler-utils
It contains pdfunite utility which can merge several PDF (Portable Document Format) files to one PDF result file.
The files are merged in order of their occurrence on the command line.
e.g. command
pdfunite file1.pdf file2.pdf result.pdf
merges file1.pdf and file2.pdf into single result document result.pdf
The package poppler-utils also contains other usefull command line utilities for getting information of PDF documents, convert them to other formats, or manipulate them: