Please find below instructions.

- Open Adobe Acrobat Reader

- Click on Edit in the toolbar at the top

- Select Preference from the dropdown list

- Select Security (Enhanced) from the menu on the left

- Untick the 'Enable Protected Mode at startup' checkbox at the top of the Window

- Say 'Yes' the warning box that apprears

- Click 'OK' at the bottom of the dialouge box.

- Close Acrobat Reader

If you are still having issues please let me know.