Not necessarily. Just set up an exception in your robots.txt document on the server, which tells the search engines to ignore that page. Blocs automatically uploads a sitemap and I wish there was a way to disable that, but perhaps @Norm could tell us if a page behind a form is automatically excluded from the sitemap. If not, you might have to manually edit out that entry from the uploaded sitemap.
EDIT: Google indexes linked PDF files by default, so even if there wasn’t a page you would have to exclude that PDF file in the sitemap and robots.txt file. Looking at this again you should probably select the option for “Go To URL” and then link directly to a location on the server like example.com/hidden.pdf