OverZip, the slick ZIP file utility for Windows, is a very easy-to-use tool that includes the compression boosting feature (OverZip Compress/Expand).
It turns out that existing compression algorithms are non-optimal for PDF (Acrobat Reader, Adobe Reader), SWF (Macromedia Flash Player, Adobe Flash Player), ZIP/JAR, PNG, JPEG, and MP3 files. The OverZip program allows to reduce the size of an archive created by popular archivers including WinZip, WinRAR, 7-Zip, and WinUHA, if the archive contains files of the types specified. To reduce the size of an archive, OverZip uses the same external program as one used to create the archive. The archive is decompressed to the temp folder, then the special files are preprocessed, and the archive is recompressed. Such recompression allows the size to be reduced by 30% and beyond.