When i start a PDF from Multicommander and with Adobe Reader, and watch it in Full screen View (Ctrl+L) and end the Full Screen View also with Ctrl+L, then is the MultiCommander on Screen and not the normal View of Adobe Reader. I have no Idea why. But this bug should be fixed. I guess it have to do with how Multicommander open Programs.
Sounds like a bug with Adobe Reader. or Windows. Or something else
When you run a pdf, MC do not know what that is. So that file is sent to Windows. And Windows find in the registry that .pdf is associated with that Adobe Reader and that is can open this and then it launched Adobe Reader with that file.
MC have NO control of that Windows does with the file that was sent to it. And after the command was sent to Windows, MC does not care anymore and continue.
Also MC never do anything to try to put it self ontop in the Window Stack. It is also not possible anymore for a normal program to force it self to be in focus anymore (Since Win7+)
I think MC pops up because it is the next windows in the Windows Stack. And something in Windows get confused and send up MC instead of AReader. Don't know why
( You seams to have some very strange issue and behaviors on your setup that I never seen before. Some thing is very different with your setup and everybody else.
The question is what. Problem is that I think it will be impossible to find out that )