I wrote a technical book using MS Word 2013. The book is in the final stage right now. Recently, I upgraded Word 2013 to 2016. If I open it with Word 2013, I can show and hide the field codes, mainly XE and TA codes. However, if opened using Word 2016, I cannot hide the codes anymore. I tried Alt-F9 and Option/Advanced/Show Document Content/Show Field Codes Instead their values, but nothing works. Can anybody give me some hints how to hide these codes? Thanks.
Edit:
I used Option/Display/Hidden Text to clear the XE codes. However, I cannot trigger it on and off using Alt-F9. Is there anyway to trigger it on and off? Thanks.

As you've discovered, the key is the display of hidden text. There is no button for turning it on or off. You could use Ctrl+D followed by Alt+H followed by Enter.

Thank you, Charles:
Right now, the only way I found I can turn it on is to make an arbitrary index. After the code XE is on, I can turn it on and off by using the show paragraph sign in home manual. However, it is odd if there is no way to turn it on in the first place.