Are you using Ubuntu, Linux Mint or other similar distributions? Do you need a program to work on PDF pages? Here is the best one that you could use: PDFchain.
To install it just open a Terminal (CTRL + ALT + T), type
sudo apt-get install pdfchain
and insert your password to enable root privilege.
When the program is installed just search for "pdfchain" in the menu: you will then be able to import one or more PDF files, select pages from them, copy them, rotate them, give them an order, even encrypt the output. Then you can merge everything in a single output PDF document.
It's really fantastic! Have a try and enjoy it!
