You can do some really cool stuff with Ghostscript on the command line on a computer running Linux or OS X. However, it’s hard to remember all that stuff when you don’t use it very often. I recently learned about a set of command-line PDF manipulation tools called PDFjam. If you are a geek like me, you probably already have pdfLaTeX installed. I can’t summarize the capabilities any better than the description on the PDFjam site:
PDFjam is a small collection of shell scripts which provide a simple interface to much of the functionality of the excellent pdfpages PDF file package (by Andreas Matthias) for pdfLaTeX. These scripts take one or more PDF files (and/or JPG/PNG graphics files) as input, and produce one or more PDF files as output. They are useful for joining files together, selecting pages, reducing several source pages onto one output page, etc., etc.