We are aware of an issue where PDF files do not open successfully from SharePoint Farm. The solution to this is outline below.
The solution to this issue is to ensure that Protected mode in Adobe is disabled.
In Adobe go to Edit > Preferences> Security (Enhanced) and untick Enable Protected Mode at startup
This setting can also be disabled through the registry editor by navigating to HKEY_CURRENT_USER\Software\Adobe\Adobe Acrobat\DC\Privileged and setting the value of bProtectedMode to 0.
This part of the solution involves creating a mapped drive to your SharePoint environment.
Creating a mapped drive to your SharePoint environment
Open File Explorer from the taskbar or the Start menu, or press the Windows logo key + E.
Select This PC from the left pane. Then, on the Computer tab, select Map network drive.
In the Drive list, select a drive letter. (Any available letter will do.)
In the Folder box, type the path of your SharePoint location. To connect every time you sign in to your PC, select Reconnect at sign-in.