Desktop search engines like Spotlight and Beagle are all the more useful if the files they index have structured meta-data. Like most audio and video files, PDFs can have some useful meta-data embedded in them. A number of Mac OS X applications provide interfaces for attaching meta-data to files, but this meta-data is not carried over to PDFs exported from the application, either by direct export or by using the Print -> Save As PDF feature.

Here is the meta-data I’ve embedded in a Pages document:

Here is what is retained when it is exported to a PDF file:

Where did my meta-data go?!

There is information such as the document’s PDF producer & version, byte size, and page dimensions. I cropped the image to focus on information most likely to be useful to users.