How to decrease .pdf size without losing quality

## Background I want to decrease size of the .pdf filled with images. In Preview in can be dome through Export and set Quartz Filter-> Reduce File Size before saving. ## Problem The file indeed decreased from ~30MB to 0.37MB. But the result has such poor quality that images are barely readable. ## Question I saw an examples of using Image Magic to achieve that - but can it be done by **Preview** without any external software?