Can I tell when a client has opened my proposal?

Yes. Kliently tracks opens and views, and the proposal's status moves on its own: sent → viewed → accepted. You don't have to ask "did you get a chance to look at it?" — you can see that they did.

That visibility changes how you follow up. A proposal that's been viewed twice but not accepted is a nudge-worthy conversation; one that was never opened is a deliverability or attention problem instead. You're following up on facts, not guessing.