How to access the cookies of the source or the parent domain in which the iFrame is loaded with different domain?

I want to read/access the cookies of the domain ( which is not owned/managed by me ) under which the iFrame of my website domain is loaded.

Let’s take an example

• The main source/parent domain is – abc.com ( not owned by me )
• On abc.com there is an iframe with src pqr.com (owned/managed by me )

I want to read the cookies of abc.com(main website) in pqr.com(iframe website)

Is this possible? if yes, how? If not, why?