I just had the need to concatenate several pdf files to a single one. Since my desktop computer is running Windows, I first tried to download and use some freeware utility. After the first one did not work as advertised and the second one tried to sideload some adware I stopped going that path and remembered that I had ssh access to several Linux boxes. So I clicked on the second Google result for “concatenate pdf” and was sent to Doei Doei which gave me the following solution:
gs -q -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=out.pdf file1.pdf file2.pdf [...]
I had to install Ghostcript (apt-get install ghostscript) for this to work, but after that, I ended up with a working pdf within seconds.
Please, nobody try to tell me again that Windows is more user friendly than Linux.