Adobe Reader 10 cannot open pdf from UNC path

If you have deployed Adobe Reader 10 and get messages saying that your users cannot open .pdf files from a network location the likely culprit is that protected mode is enabled.
You can turn this mode off using a registry edit as below:

Registry Editing Method
Open notepad and paste the following command, when pasted save as a .reg file.

REG ADD "HKCU\SOFTWARE\Adobe\Acrobat Reader\10.0\Privileged" /v bProtectedMode /t REG_DWORD /d 0 /f

Alternative Method

If using Server 2008R2 you can set a preference to make a change to the registry for users as below

Open Group Policy Management from Start > Administrative Tools > Group Policy Management

Create a new Group Policy Object

Give the GPO a suitable name

Right click and select edit

Expand the User Preferences menu option

Expand the Windows Settings and select Registry

In the blank area in the right hand pane right click and select New > Registry Item

Ensure that the settings are to ‘Update’ the registry key, also check that the selected hive is HKEY_CURRENT_USER.

In the Key path enter ‘SOFTWARE\Adobe\Acrobat Reader\10.0\Privileged’

Enter ‘bProtectedMode’ into the Value box

Change the value type to REG_DWORD

In the value box enter ‘0’

Click OK and you are done.

This is how the finished registry entry should look.