Issue:
User opens a .ppsx file from SharePoint or other network location and the file opens in PowerPoint full application. Users want the file to open in Slide show mode.
Workaround:
This behavior can be modified by making a registry change.
**Registry changes can be dangerous if not done correctly, you assume all risks for editing the registry.
Open Regedit.exe
Navigate to Key "HKEY_CLASSES_ROOT\PowerPoint.Show.12"
edit value BrowserFlags
Set the value to be 8
The possible values are
a = open in edit mode
8 = open in show mode in new window
0 = open in show mode - this opens in the browser, I would not recommend this, the power point process could possibly get stuck and stay running even after the slide show ended.