Harness the power of Spotlight. By Adding keywords to your PDF files, you can improve your search results by adding specific keywords to your PDF file. Here is how to do it: 1. Open a PDF file with 'Preview' 2. Choose 'Tools -> Get Info' (or press Command-I) 3. Select the 'Keywords' tab. Click on 'Add' and enter in specific keywords. Use words that you are likely to use when searching for this document. Add as many as you want. 4. Close the window. 5. Choose 'File -> Save'. Now, give your keywords a try. Do a Spotlight search and check your results.