I've had a similar problem and it was solved by downloading and installing the standalone version of Adobe PDF Reader DC from rocketfiles.com. Also, try to open the same file using the Dropbox website or open it with the desktop tool. Do not forget to close the VPN. Sometimes the problems may occur because of such IP changes-manipulations.
The way we work is changing. Share and discover new ways to work smarter with Dropbox in our community.Sound good? Let's get started.