I asked that question myself for other submissions several times. It happens that I start to write a comment, post it and find that the submission was flagged and disappeared from the HN home page while I was writing. Sometimes they feel like absolutely innocuous submissions. I wish there is an unflag link, not the one to undo one owns flag requests (which happen due to fat fingers and tiny links.)

> I wish there is an unflag link, not the one to undo one owns flag requests

The "vouch" link works like this: https://news.ycombinator.com/newsfaq.html#cvouch

I guess for whatever reason this one was flagged? Seems enough people consider it not-relevant.

probably because it's a pdf on dropbox, which can't really be trusted to be legit

I may be out of the loop, but I don't understand the negativity towards Dropbox links, what makes it different than other submission of PDF files?