jPDF Tweak is a Java Swing application that can combine, split, rotate, reorder, watermark, encrypt, sign, and otherwise tweak PDF files. You can use it to make printable booklets from your PDFs, to add PDF bookmarks, effects (page transitions), to combine multiple PDF files, to watermark them, to rotate pages that do not fit, to attach files to your PDF, to encrypt and sign your PDFs, to change metadata (like author or keywords), and much more.