What happens if you adopt a religion but not found one?

Will I still be able to get a pantheon and all of the other bonuses that come with founding a religion?

if you get your own Pantheon but don't go on to founding a Religion, once someone spreads their Religion to you, that city of yours will lose its Pantheon (and w/e benefit it was) and yes that city will begin to receive any applicable bonuses of this Religion.

however, some founder/follower beliefs of Religions are pretty stingy and only really benefit whoever founded it. someone had broken the specifics on this issue a while back, but it's kind of an old thread now i think.

Here’s two current threads on this topic:
I'm in the habit of building Stonehenge EVERY game
Why I have stopped founding religions altogether

tldr: By not founding, you miss out on founder benefits, but those are relatively weak. By not founding, you will not get CS requests for conversion, maybe not a big deal to you. The religion you are adopting comes with a pantheon and two follower benefits, but you will loose any pantheon belief you have picked up. By adopting, you might well be able to pick a religion with better bonuses than you would get from founding late.

You get that religion's pantheon, two follower beliefs as well as its reformation belief (if any). You also get a diplomatic bonus with the religion's founder, which disappears by the industrial era, and the founder gets a 25% tourism bonus towards you (which can be enhanced to +40% through Aesthetics).