How to Fix Adobe Reader "Invalid Plugin" Error
Purpose: The purpose of this article is to teach you how to fix the "Invalid plugin detected, Adobe Acrobat Reader DC will now quit" error that may occur when opening a PDF from Microsoft Outlook.
^^ This is what the error looks like ^^
1. Open Adobe Acrobat from your Start Menu.
2. Click the three lines at the top left of the Adobe window.
3. Then click on the preferences down at the bottom of window.
4. On the "General" page, uncheck the box that reads “Show Online Storage When Saving Files”
5. Scroll down to the "Application Startup" section and place a check mark on “Use Only Certified Plug-ins”
6. On the left menu click on "Security (Enhanced)". Uncheck the box next to "Enable Enhanced Security".
7. Uncheck the box next to “Enable Protected Mode at startup”. Click Yes on are you sure you want to continue.