This is not a processMax problem. But the way to fix it is the following:
For pdf files, open Adobe Reader, navigate to Edit/Preferences. Select ‘Internet’ from the Categories list. Uncheck ‘Display PDF in browser’.

If you are using IE 11,  go to Tools/Manage add-ons/Toolbars and Extensions and set the Status of Adobe to 'Disabled'.

Also, make sure that you have followed the instructions in ‘Configuring Client Computers’ found on the home page of the processMax Support Center.