I have been using the Fill and Sign app for iOS for 2 years now. All of a sudden today it no longer shows up as an option on my phone when I open a Word Document (.docx). And if I go directly into the app and try to open a Word Doc directly, they are all greyed out on my phone.
What happened? Are Microsoft Word files no longer supported?
Looking at your issue description, it seems you were working with word document within Adobe Fill & Sign app? Which is practically impossible, because Fill & Sign only supports .pdf file format. So, how did or would you fill in word file I'm not sure about that.
May be there's some confusion, you have had your word file, which was converted to .pdf and then you filled it.
So here, the answer of your question "Are Microsoft Word files no longer supported"? would be No. Microsoft word files were never supported in Adobe Fill & Sign app. Unless, its not converted to .pdf format.