These sites do not work for free downloads of pdf files:

Download Instructions:
http://nitroflare.com/

(Closed Filehost) https://uploadrocket.net
https://rg.to/file/

Is anyone else having the same problem? I just get endless pop-ups and virus warnings and end up with nothing!

This is frustrating. A couple of sites that work well for free downloads are Tusfiles and Zippyshare. I wish these were used more often.

[Tidal]

You will find this topic helpful with respect to downloading from different file hosts:
viewtopic.php?f=19&t=649944
Includes images showing what areas on the host site to click and, just as importantly, what to avoid clicking.