Pdftk is a command-line tool for doing everyday things with PDF documents:

• Merge PDF documents
• Split PDF pages into a new document
• Fill PDF forms with FDF data and/or flatten forms
• Apply a background watermark
• ...

Pdftk allows you to manipulate PDF easily and freely. It does not require Acrobat, and it runs on Windows, Linux, Mac OS X, FreeBSD and Solaris.  Pdftk is free software (GPL).