PDFsam is a free, open source, platform independent tool released under GPLv2 license and designed to perform split, merge and other manipulations on pdf document. It’s released in 2 versions, basic and enhanced.

Requirements:
Java Runtime Environment 1.6 or higher

pdfsam basic:

A simple tool designed to split and merge pdf files. With it’s simple and intuitive interface you can:

• split your pdf documents (into chapters, single pages, etc.).
• merge many pdf documents or subsections of them.
• extract sections of your document into a single pdf document.
• mix alternate pages taken from two pdf documents in straight or reverse order into a single document.
• rotate pages of the selected pdf documents.
• visually reorder pages of a selected pdf document.
• visually compose a document dragging pages from selected pdf documents.
• save and load your workspace to automate your recurrent jobs.
• manage pdfsam settings and set a workspace to load at start up.

pdfsam enhanced:

This is the enhanced version of pdfsam. In this version you’ll find all the basic features plus:

• encrypt your pdf files (RC40 bits, RC128 bits, AES128 bits) and set permissions on them.
• add a pdf frontpage or an addendum (or both) to your pdf documents.
• decrypt pdf documents.
• extract attachments from your pdf documents.
• set viewer options to a document to tell the viewer application how should open the document.
• set the metadata of a document (author, title, subject and keywords).

Check the FAQ for more details.