Fortunately someone created a GUI interface for pdftk called PDF Chain, so if you have trouble remembering the command line syntax for the pdftk terminal program, you might get most of what you need from pdftk using PDF Chain. PDF Chain is a graphical user interface for the PDF Toolkit (pdftk). The package includes features designed to handle PDF files in a easy way. Basically it can merge, split, add backgrounds or stamps and add attachments. There are some tools for extended needs too.
PDF Chain can be installed from the Ubuntu Software Center.