The opening screen (or front of the card) of this Valentine features 14 numbered doors with cupids delivering love letters through the mail. What the doors reveal is totally up to you. While the download file has already been preset with images and text - you can easily change these. (The first image below shows the doors - and the second image shows a couple of doors still closed but others revealing images and text).
I haven't had a chance to explore this myself, but I think it would be fabulous to do a version on actual paper. Basically, you would print screen the scene with closed doors, and then print screen the scene with all items revealed. On just the front image, cut in such a way that the doors would swing open. And again, you can customize the back image to contain your own text, images, photographs, etc. Glue the two pieces together around the frame of the doors - and you've got a cool interactive Valentine! (The image below is a mock-up of how this might appear, doors ajar):
If you want to do use this digitally on PowerPoint, this help article (How to create a personalized Advent calendar), while it actually discusses a similar type of PowerPoint template, (an Animated Advent Calendar I had created for Christmas), the basics hold true for updating this Valentine.