How to compress a pdf file

There are numerous online services that will compress files for you, such as this one from Adobe.

According to the PDF spec, there are up to five different internal compression algorithms used when a PDF is initially created and dependent upon the content type to be compressed. Your PDF may already be at or near its maximum compression and compressing it further may degrade content clarity.

You want dramatic compression? Then use lower resolution and fewer images in the original document that produced the PDF. No external compression tool will be as effective at size reduction than original document choices.

Bomiboll wrote:

It is not free of charge. I am not going to pay

I am able to compress a PDF without ever paying/signing in on that website. When does it prompt you to do so?

If it asks you to make an account, open a new private Safari tab (CMD + Shift + T) or clear your website data and try it again.

Or, just try another tool. A simple web search for compress pdf online yields numerous results.