A PDF carries more than its pages. This tool reads it and tells you what it found: what is active, what identifies you, and how many earlier versions are still sleeping inside.
What it does not do: An inspection does not tell you a document is safe, it tells you what we could read in its bytes. A PDF whose objects are compressed can hide active content from this scan, and the report says so when that is the case. The safety of this site does not come from that reading: it comes from the fact that nothing from a document is ever executed, and that everything leaving here is rebuilt page by page.
Nothing is uploaded. Cut your network connection once this page has loaded: the tool keeps working. How to check it yourself.