The apps Formatting tab may disappear from time to time - usually due to a Word crash.
The fix outlined in this post below is the most likely solution.
A less likely solution, but also possible is that you have an old template. The solution to this problem is described under the APPS FOR OFFICE Error Messages forum: http://appsforoffice.freshdesk.com/discussions/topics/4000310821
When MS Word starts again it will often give you a message that will read something like: "... the apps Engine addin caused a serious problem last time Word was running, do you want to disable this addin?"
If you answer Yes, Word will hide apps Formatting and the orange won't work either.
To reset MS Word, you will need to display your Developer tab.
For Word 2013, here are the quick instructions - for other versions it is similar.
You do this by select File > Options > Customize Ribbon and tick the Developer tab in the right hand panel.
Click OK and you will see the Developer tab when you return to MS Word.
Click the Developer tab.
Click the COM Add-Ins button.
Make sure "appsEngineV2" is checked.
(NOTE The version number will be different for new versions).
Exit MS Word.
Start MS Word and the apps Formatting tab should now be displayed.
Note, if apps Formatting is still not displayed, MS Word may have seriously disabled the apps Formatting/apps Engine addin.
In MS Word, return to File > Options
Click the Add-Ins item
Scroll down to the bottom of the Addins lists and you may see apps EngineV2 in the Disabled or Inactive addins list.
Towards the bottom of the screen, click on the Manage drop down.
Select "Disabled Items"
If the appsEngine addin is in the list, enable it.
Start Word again.