The first step to compressing a PDF file is to take stock of the situation: what has increased the file size so much, what can and cannot be reduced. For this, go to Advanced> PDF optimizer> Audit space usage in the Adobe Acrobat software. The software will provide you with a list of items and how much space each of them occupies. These will be images, bookmarks, content streams, fonts, structure info, link annotations, document overheads, color spaces and extended graphic suites. Some of these, like images and content streams, will occupy much more space than the others.
Planning what to retain and what not to retain:
Some of the contents like content streams and structure info can never be reduced without totally messing up the document. Some, like bookmarks, link annotations, document overheads, color spaces and extended graphic suites are modifiable, but it takes a lot of expertise and careful planning to do so, and modification is not recommended. Some others like font and images you always need to compress as much as possible to compress a PDF file. You need to keep this in mind when you compress your PDF file.
Using the PDF optimizer to compress a PDF file
The best way to compress a PDF file is using the PDF optimizer, especially where it comes to images, because pre compressing images can create compression artifacts when distilling them in PDF. The PDF optimizer tool has various features, including images, scanned pages and fonts, transparencies, discard objects and clean up of the final out put that is created. Each of these help reduce the size of a PDF file in some way, by attacking one or more of the issues that vex the PDF creator and increase its size.