While there is no "official" standalone PDF download provided directly by Nintendo for free, several digital resources exist:

Rosalina’s Storybook remains a landmark in the Mario franchise. It transformed Rosalina from a simple "deity" figure into one of the most relatable and beloved characters in the Mushroom Kingdom. Whether you are reading it in Super Mario Galaxy or via a digital archive, its message of finding family among the stars continues to inspire players of all ages. AI responses may include mistakes. Learn more

The story follows a young girl (young Rosalina) who builds a spaceship to chase a mysterious white star. She finds a wounded baby Luma. Together, they travel the cosmos. The central tragedy is her recurring dream of her mother baking a cake. Eventually, her mother’s voice fades, and the Lumas become her new children.

If you are looking to write a paper on this story, here are four "outside the box" angles that look at its psychological and structural impact: Rosalina's Storybook - Super Mario Wiki