Start Anim8tor.

File / New.
Import your first OBJ.
Select toolbar icons - Object viewpoint and Frame view.
Your object should now be visible.

then..

File / New.
Import your next OBJ.
Select toolbar icons - Object viewpoint and Frame view.
Your object should now be visible.
Select toolbar icons - object edit and select. Click cursor on object to select it.
Copy it (cntrl+c).
Switch back to your other window/file.
Paste.. (cntrl+v).
Both objects are now in the same window/file.

Hope this helps !

Gerald