A blog by Devendra Tewari
To merge or join pdf files with ghostscript, from the command line
"c:\Program Files\gs\gs9.06\bin\gswin64.exe" -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=join.pdf -dBATCH ch01.pdf ch02.pdf ch03.pdf ch04.pdf ch05.pdf ch06.pdf ch07.pdf ch08.pdf ch09.pdf ch10.pdf ch11.pdf ch12.pdf ch13.pdf AppA.pdf AppB.pdf
Change the command appropriately for your operating system and files.
A pity gsview does not provide a GUI for doing that.