Meds, I think it might be because you are using Word from a location Microsoft does not recognise as "You" so it wants confirmation to let "you" use "your" version of Word - annoying, eh?
I am not a user so not sure but it looks like a common problem and none of the "fixes" I have found seem to work. You either bite the bullet and sign in or use something else. If you try to sign in but have forgotten your password there should be a password reset option to send a link to your email address.
As an
alternative. It's what I use and it works with .doc and .docx file formats - also Excel and PowerPoint. A couple of things to change. When you open TextMaker, the Word alternative, go into Tools>>>Appearance>>> untick Use Automatic Hyphenation. Now go to Files>>>Default file format>>> from the drop down choose MS Word 2007-2016(.docx) and make a note of the Template and Backup folders, click OK and you are done.
You can also send files to any folder you like by using File>>>Save As to keep your work local - make sure to opt for Word Document as it defaults to rtf.