Edit, Merge, Modify Your PDF Files : jPDF

jPDF is a very simple. light yet powerful tool that enables you to modify your pdf files by customizing them with watermarks, re-arrange the bookmarks, or change the page size, using password protection personalizing how a PDF file is opened and many other options.

The application is available for free download but you must have Java Runtime Environment installed on your machine.The simple tool compromises on the looks and comes with 11 tabs used for different purposes.
In the first tab you can merge the pages with options like manual feed and automatically selecting even/odd input. You can also change the page orientation with this java applet. A personalized watermark can be added to each page of your pdf document.

You can edit and add bookmarks and add transition effects when a page is turned.The document information like the name of author and other such information can also be tweaked.
jPDF is capable of adding password protection to your documents and can set various permissions for different users.

Try it now. Download here.