Out of the six cats we have had, three have been very adept at opening doors. I hate cats in my closet, getting fur on my clothes, so we had to figure out how to keep them from opening the sliding glass doors. I came up with a hook and yarn closure to keep the doors from being opened by little paws.
The best story I have of one of our cats was my first cat, an anniversary present from my hubby, who liked opening the guest bathroom door, which was a sliding pocket door. We had an exchange student and her first night in the house, she used the guest bathroom. While on the toilet, the door suddenly started to open and she was terrified she was in a pervert's house, when she noticed it was just the cat being nosy. She kept the door locked after that whenever she used it!