How to get back old configurations of app windows if lost because of reboot? Macbook froze (the rainbow beachball was just twirling) because of low memory, so I needed to do a reboot using the power button. 

Might have done a safe mode reboot (not sure).

After I restarted all of the windows, PDFs, etc where not back on the screen. Restarted again choosing not to start up with the same windows, hoping the old setup would appear again.

This time some app windows such as Evernote and Safari was back to normal but not the PDFs. 

Is there some way to get back the old setup of app windows? Perhaps with Time Machine or some backup cache.
By opening up the OSX preview app there is a chance that the PDFs will show up again. That worked for me.