For most users, downloading the file is the best option. It is small (usually under 100KB), easy to edit, and simple to use.
This is a gray area. Downloading a subtitle file ( .srt ) is in most jurisdictions because it is a text file containing timecodes and dialogue. However, using it to watch a pirated copy of The Martian does violate copyright law. If you own the Blu-ray, DVD, or a legal digital copy (iTunes/Amazon/Google Play), downloading a matching SRT file for personal use is generally considered fair use for accessibility. The Martian English Movie English Subtitle Download