If you are using macOS Mojave 10.14, you can continue to use Office 2011/2016 for Mac. However, when you upgrade to macOS Catalina or later, you will need one of the Microsoft 365 (subscription), or Office 2019 for Mac (single-purchase) 64-bit application suites. Or the free LibreOffice Suite which is a superset clone of MS Office.
Pages is not a Word clone, and when you open a Word document, it is translated into an internal Pages document format without making any changes to the Word document. When you want the Pages content back in Word format, you must export it to Word. This too is a translation process and the exported Word document may look nothing like it does in Pages, or as it did before it was opened. This is the peril of translation, something you would not have to deal with if using MS Word, or apologize for if you are sharing Word documents with other Word users.
The current versions of Pages, Numbers, or Keynote that are in the Mac App Store now require macOS Catalina or later, and cannot be installed on macOS Mojave.
These are fellow user supported communities and not Apple-badged support.