ORPALIS PDF Reducer is an interesting tool which optimises PDFs to cut their file size by up to 80%.

This isn't another tool which just cuts document resolution, either: PDF Reducer uses multiple tricks to do its work.

If the file contains scanned documents then it may mix colour and black and white pages, for instance. PDF Reducer detects the black and white images and encodes them as plain B&W, often with dramatic savings.

The program examines individual PDF objects, removing any which aren't used, and resampling unnecessarily high resolution images.

PDF Reducer also applies multiple compression techniques on some images, reducing file size without losing any quality.

There's support for linearization, too, which enables large documents to be viewable by web users before the complete file has downloaded.

All this is easy enough to set up, and at a minimum you could just point PDF Reducer at your source files, give it an output folder, and click a button.

Please note, though, ORPALIS PDF Reducer has a very annoying nag screen. If you're launching a big batch processing task then it'll start as normal, but after every 5 documents, all work is stopped, the nag screen appears, and there will be a countdown of several seconds (up to 12 in our tests) until you clear it. After that, you get a few more seconds of processing before it's paused again.

The finished documents can be significantly reduced in size, and there are no watermarks or other catches. But if you're going to be regularly batch processing large numbers of PDFs, the constant interruptions are going to be a major hassle.

The Professional Edition removes the nag screen, adds a command line interface, multi-threading support, and accepts almost 100 input formats, too (it becomes a super-efficient "anything > PDF" converter). It's yours for $199.