My cat spent the first year or so of his time with us plotting a Mission: Impossible style ingress into my home office. The tricky bit has been finding a way to the exposed ventilation pipe in our loft, from which he could hop through the high-up, paneless window into my office. He attempted literally climbing the walls, and investigated the possibility of hopping on the blades of the ceiling fan to reach the pipe. (Thankfully, he never hopped on said blades, only stared at them and attempted to trace a path back to a perch he could reach.)

I'm fairly certain he knows one could simply use the door handle. It's only a question of height and weight. He can reach it with his paws now, and it's only a matter of time before he figures out how to shift his weight to pop that door open...