In Acrobat, you can create a lower-resolution version of an existing high-resolution PDF file by simply choosing File> Reduce File Size or Document> Reduce File Size. This downsamples all your images to 150 dpi, suitable for on-screen viewing or desktop printing.
For an even smaller file, use a different tool: PDF Optimizer from the Advanced menu. In the PDF Optimizer window, downsample images to 72 dpi and choose a JPEG quality level (JPEG affects only the image preview in the PDF). You can also choose to unembed fonts if you like.
If you have many files to shrink, choose Advanced> Batch Processing and click the New Sequence button. Give your new Sequence a name, click the Options button, and then enable the PDF Optimizer checkbox. Then, click the Settings button and set up PDF Optimizer the way you like.
When you click the Run Sequence button, Acrobat will prompt you for files to process.
Jay Nelson is the editorial director of PlanetQuark.com, and the editor and publisher of Design Tools Monthly. He’s also the author of the QuarkXPress 8 and QuarkXPress 7 training titles at Lynda.com, as well as the training videos Quark includes in the box with QuarkXPress 7 . In addition, Jay writes regularly for Macworld and Photoshop User magazines and speaks at industry events.