Word 2016 cannot hide field codes in document created by work 2013

[twinclouds]

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.