Are you referring to the new tabbed view in Acrobat DC?
Agree, this a downgrade, the older versions had a document menu that has gone, my opinion the program is not worth the £300 UK pounds.
There is no possibilities on going back
Just because the "Document" menu is gone, that does not mean that the functionality is not there anymore. BTW: This is not a new change, this menu was removed back in Acrobat X.
You can find the different items that used to be in Document menu in more logical places: All page related items are e.g. in the "Organize Pages" too:
If you don't know where to find a certain tool, use the search function:
It's all still there, and you actually have more functionality in Acrobat DC than you had in Acrobat 9.