Dropbox's CEO declared it as a fact last year and it has been widely reported:

https://www.bloomberg.com/news/articles/2016-06-14/dropbox-c...

https://www.wsj.com/articles/dropbox-ceo-were-cash-flow-posi...

https://techcrunch.com/2016/06/14/dropbox-says-it-is-cash-fl...

But I have not personally inspected their financial statements and conducted an audit to confirm this with my own two eyes, if that's what you're asking.