If you have a Mac, there is a great and easy way to significantly reduce the size of a PDF file using the built in Preview app. It also supports encrypted PDF documents and can work on a batch of hundreds or even thousands of PDF files at once. It supports lossless compression, so you should not see any reduction in the quality of the PDF.
PDF Compressor is a free program you can download for Windows XP/Vista/7/8 that lets you quickly and effectively reduce the size of one or many PDF files. In addition, you can remove bookmarks, remove PDF layers, remove annotations, remove page labels and manually adjust the quality for color and monochrome image compression.
