The problem is usually caused by proxy / firewall that interrupts the communication between the content and authentication server.

To resolve this issue, please ask your IT department to whitelist the domain protectedpdf.com on port 443 (https) and/or port 80 (http) for old content.

Why proxy servers affect the process:

Proxy servers are designed to protect your organization from unwanted viruses, malware and other phishing type schemes. However, some types of communication is warranted, such as the content you're trying to access from a legitimate and trusted source. 

Proxy server required configuration changes:

1. The proxy MUST allow direct communication
2. With the DNS address https://protectedpdf.com/, http://protectedpdf.com/, and https://api.protectedpdf.com/
3. On ports 80/443

Firewall required configuration changes:

1. Remove any blocks in Norton or other firewall software for
2. https://protectedpdf.com/, http://protectedpdf.com/, and https://api.protectedpdf.com/
3. The firewall MUST allow communication with
4. https://protectedpdf.com/, http://protectedpdf.com/, and https://api.protectedpdf.com/

Adobe/Acrobat Trust Manager configuration changes:

1. Open Adobe/Acrobat
2. From the top menu bar, select Edit > Preferences
3. Under Categories, click Trust Manager
4. Click the Change Settings button
5. Remove any blocks to https://protectedpdf.com/ or https://api.protectedpdf.com/ 
6. Allow communication with https://protectedpdf.com/ or https://api.protectedpdf.com/

How to check for a proxy server:

1. Open Internet Explorer (not Firefox or any other browser)
2. Select Tools > Internet Options
3. Select the Connections tab
4. Click the LAN Settings button
5. Check to see if the "Use a proxy server..." box is selected

Special consideration:

If you have a customized domain name, other than Vitrium's protectedpd.com, then your domain name(s) would need to be whitelisted instead.