Just use MS OneDrive to store your files. Than to open just use MS Office online, it's free. Though I suggest a 365 subscription as you get 1TB of cloud storage for OneDrive. The online version is actually pretty awesome and I use Word and Excel everyday.
(you must have an Outlook or Hotmail email account, free to setup)
If you need the actual MS Office for Windows, you will have to install Ubuntu under ChromeOS, than install Wine, than MS Office. It's not as hard as it sounds, just search for "install Ubuntu Chromebook", than "MS Office Wine". You can also install VMbox, than create a Windows virtual machine to run Windows applications.
There is MS Office for Android which is the same version you get for the iPad.
There are also online services that will stream applications like MS Office to your ChromeBook. Though they stream Linux applications, check out http://rollapp.com/apps
to see what I mean.
I personally made my own streaming service by buying a small Intel NUC Canyon, i7 8th Gen, x2 32GB Ram, x2 1TB M.2, internal GPU; Vega64m, external GPU; Nvidia 2080ti and than installed Citrix's Application Server on it. Now I can stream any application (Windows/Linux/OSX) to my PixelBook ChromeBook, Samsung Tab S4 DEX or Samsung Note 9 DEX. The Note 9 with DEX is actually my desktop computer, when inserted into its dock, it connects to a 4K touch monitor, mouse, keyboard, external HD, printer, Wacom board and even a 3D printer. All works as if I were using an actual Windows computer, but it's my phone.
Cool stuff and people wonder why I think the iPhone feels so archaic.