a simple and free way of reducing pdf file size using preview

Compress a PDF

To save storage space, you can compress a PDF in Preview. When compressed, the PDF may be of lower quality than the original.

1. Open the PDF, then choose File > Export.
2. Click the Quartz Filter pop-up menu, then choose Reduce File Size.

najm_ahmed wrote:

How to control the quality. The pdf after compression is hardly readable

I have not found a free application that reduces pdf file sizes well, maintaining resolution well. Maybe someone can recommend a free one here. However there are several applications that must be purchased that do this well, most seem to cost between $75 and $100. I have used PDF Expert and it does this very well, reducing PDF files from 35 MB down to 1 MB and in this instance, I could not see a difference in sharpness or quality. Adobe Acrobat can of course do this but is more costly, although there is a lower price for the student/teacher edition.

How to control the quality. The pdf after compression is hardly readable

Good question

Yes, it's due to the graphics & how much you reduce it by, if you can reduce the pics then it'll be much smaller to start with.