Files with the extension rst are reStructuredText files, a plain text format used by Python to generate documentation with more complex formatting. They can be used with the Docutils library, but if you're looking for a quick and easy to convert .rst files, try installing the RST (reStructuredText) Viewer and Editor app for Chrome.
Enter the text from the .rst file on the left, click the 'View as PDF' button at the top, and on the right a formatted PDF will be generated.