Check out Extracting metadata from multiple PDF documents by noreply@blogger.com (Craig Haiss). Here is an excerpt:
Adobe Acrobat allows you to add metadata to your PDFs, and the values you assign to these tags will be available for search engines and other services that rely on metadata. For example, you could add a value called “author” and assign the name of the document’s author to that value. Also,…
The full article is available here.