jPDFSecure is a Java library which can digitally sign PDF documents and change security settings on PDF Documents. With jPDFSecure, your application or Java applet can encrypt PDF documents, set permissions and passwords, and create and apply digital signatures. jPDFSecure is optimized for performance and is built on top of Qoppa's proprietary PDF technology, so there is no need for any third party software or drivers. jPDFSecure has a simple interface to load PDF documents from files, network drives, URLs, and even input streams, which can be generated at runtime or come directly from a database. After changing security settings, jPDFSecure can save the document to a file, a java.io.OutputStream, or a javax.servlet.ServletOutputStream when running in a J2EE application server to output the file directly to a browser. jPDFSecure is platform-independent and can be used in any environment which supports Java.

URL: jPDFSecure | Java PDF Security and Sign Library | Digitally Sign PDFs, Set passwords & permissions with Java