https://articlescad.com/how-to....-install-a-cat-flap-
Cat flaps are a great way to let your pet come and go at their own pace. You can opt for a lockable flap to prevent other animals and cats from entering your home. You can install an animal flap inside a bifold door as long as the door is composed of toughened glass and the frame isn't rotten or damaged. The process is similar to installing a cat flap on an old wooden door or uPVC. Easy to install Install a cat flap onto your bifold door, allowing your pet to exit and enter the home without needing to open or close the door.