1, we can't see the words behind the paper, not only because the paper fibers block the line of sight, but also because the fibers are full of air (not bubbles), because there are holes invisible to the naked eye inside the fibers, and these tiny bubbles form diffuse reflection with the fibers to block the light. When water drops on paper, water will expel air, but it will also dissolve some fibers (few) and change the physical structure of fibers (so dry them).

2. Where the water slides, the physical structure of the fiber changes, which makes the water resistance smaller, so it is easier for the water to come back from the previous sliding place. But it is not absolute. The path of water is influenced by many aspects, even the rotation of the earth.