See the section "Screen selector" in mc's manual. It mentions the three relevant shortcuts: Alt{, Alt} and Alt`.
Viewers and editors open their screens. E.g. press F3 to view a file, and instead of quitting by the usual F3, F10 or Q, try pressing Alt{.
It looks as if you've quit, but not, you've just temporarily switched back to the main screen. By using the shortcuts mentioned above, you can get back to the viewer, at the position where you left it.
You can have as many viewers and editors open at a time as you wish, however, you can't have multiple file managers.