Word 2016 and Excel 2016 - Customize the File > Open menu

Any clue how I could get my old menus back without the useless ribbon ?

Unfortunately this is one place where MS went out of it's way completely eliminate backwards compatibility.  It would have been trivially simple for them to keep the menu code, and update it as needed, but instead they decided to rip it out completely.  It is funny, and sad, in light of this security bug that was just revealed. It affects EVERY version of Office AND Windows since Windows 95

2017 11 15- Office security bug discovered after 17 years and what you must do

https://office-watch.com/2017/office-security-bug-discovered-17-years-must/

So, there is no way in Office to recover those lost menus.

I have not looked in 3 or 4 years, but one of the very first 3rd party addins that were released for Office 2007 were tools to restore the menu to the application, with varying levels of success.  I did try them in 2007 and 2010, but finally gave in and just used the ribbon (but I do still hate it, and my "muscle memory" still does use Menu shortcuts that may no longer apply.

Here are links to some of the original addons. You'll have to check to see if they still work on 2016

http://www.addintools.com/english/menuword/default.htm - menu addin 2007 only, free trial

http://www.ubit.ch/software/ubitmenu-languages/ - 2003 menu added to ribbon

http://software.techrepublic.com.com/abstract.aspx?docid=862867&promo=100511 – Classic Menu for Office 2007 ($30)

http://news.office-watch.com/t/n.aspx?articleid=799&zoneid=12 – a review of UBitMenu

http://www.addintools.com/english/menuoffice/default.htm - Show Classic Menus and Toolbars on the Ribbon of Microsoft® Office 2007

http://www.indelibleink.com/WordMenu.html - Free version of 2003 menu addin.  There are several different install options, quite cool.  Installed cleanly on my admin ID, but not in my user ID.  Installs a template in the C:\users\USERID\AppData\Roaming\Microsoft\Word\STARTUP folder.  WordMenus.dot is the 2003 menu alone.  WordMenu.dot is the 2003 menu with the standard toolbar.  WordMenusTB is the vertical orientated 2003 menu.  It looks like this

http://software.techrepublic.com.com/abstract.aspx?docid=927295 - Saavvii for Microsoft Word 2000, free to try

http://www.toolbartoggle.com/Contact.aspx - ToolbarToggle ($20) - 2 modes, full toggle replacement for Ribbon or Adds new tab to ribbon.  Allows customization of menu portion, adding macros using right click “customize togglebar” feature, not Word customize.  I haven’t tried it, but if it lives up to propaganda it looks best yet.  5 day free trial.

http://software.techrepublic.com.com/abstract.aspx?docid=847883&promo=100511 – Ribbon Customizer for Office 2007 ($40)

http://word.mvps.org/FAQs/Customization/CustomizeRibbon.htm Customizing the Office 2007 user interface. Info about 2 purchased addins, Ribbon Customizer™ and ToolbarToggle™ add-ins for Office 2007.  They also have limited functionality trial versions

If you don't like the ribbon, you could minimize it using the arrow at the far right n the ribbon. You can restore it by the same arrow in reverse. Then, since the quick access ribbon at the top of the screen is more like a menu that you might be comfortable with, you could customize that to have your commonly used items on it. The quick access menu is at the upper top left of the screen and there is a customize function by clicking on the drop down (down arrow).

Hope that helps.

You can't, the ribbon interface is here to stay, at least until they find something better.