The Brainliest Answer!
As the paper has cellulose content, the cells (which are high in cellulose content) absorb water and hence a bulge is formed.

1 5 1
i don't know if this answer is correct as in paper the cells are dead so they do not absorb water
but still if I believe that they absorb water if i bake it or keep it in extreme heat it should come back to its original state
I think in a way your answer is correct
I will research on this more to find the correct answer
but still thank you very much for helping me