From PDF Labs:
If PDF is electronic paper, then pdftk is an electronic staple-remover, hole-punch, binder, secret-decoder-ring, and X-Ray-glasses. Pdftk is a simple tool for doing everyday things with PDF documents.You can merge PDF Documents,split PDF Pages into a New Document,rotate PDF Pages or Documents,decrypt Input as Necessary (Password Required),encrypt Output as Desired,fill PDF Forms with FDF Data or XFDF Data and/or Flatten Forms,apply a Background Watermark or a Foreground Stamp,report on PDF Metrics such as Metadata, Bookmarks, and Page Labels,update PDF Metadata,and attach Files to PDF Pages or the PDF Document.
Unpack PDF Attachments
Burst a PDF Document into Single Pages
Uncompress and Re-Compress Page Streams
Repair Corrupted PDF (Where Possible)