Tor.com (the publisher) gives away free eBooks every month. Mistborn has appeared on this list twice. Sign up for their newsletter. By the time you find a working Reddit link, Tor might have legally emailed you the file.

Happy reading, Rust and Ruin.

If you are searching for a "hot" PDF because you left your hardcover at home, Reddit will likely forgive you. If you are searching because you just don't want to pay $7.99 for the ebook, the downvotes will rain upon you like ash from the Ashmounts.