How can I change the resolution of a PDF I have scanned a document into a PDF at 300dpi.  The document file is larger than I would like.  Is there a simple way to down-sample the document so that it has a lower resolution?  Or do I just need to re-scan the original document?
You can use ImageMagick's scale or resize operators.


  ImageMagick® is a software suite to create, edit, compose, or convert
  bitmap images. It can read and write images in a variety of formats
  (over 100) including DPX, EXR, GIF, JPEG, JPEG-2000, PDF, PhotoCD,
  PNG, Postscript, SVG, and TIFF.


For example, from a terminal:

convert input.pdf  -resize 50% output.pdf


or

convert input.pdf -scale 50% output.pdf