This is how the SHA1 collision PDF format trick works (it's really an embedded JPEG format trick)pic.twitter.com/ogPuPegKL6
You can add location information to your Tweets, such as your city or precise location, from the web and via third-party applications. You always have the option to delete your Tweet location history. Learn more
Except it's a JPEG trick, not a PDF trick... The PDF part is just because I guess they preferred a document format.