http://uwb25d43nnzerbozmtviwn7unn7ku226tpsjyhy5n4st5cf3d4mtflqd.onion/posts/metadata/index.html
A PDF file may have information about what program created it, what computer, etc. This can be used by investigators to link a photo to the camera on which it was taken, a video to the computer on which it was edited, and so on. Before you put a sensitive file on the Internet, remove the metadata.