A User of Insert icons for Docs
To all those whose isn't working - it isn't available or visible on .docx files you uploaded to Google Drive. It took me a few minutes, but your file HAS to be in Google Docs format. So if you uploaded a file .docx file (a Word doc), just open it with Google Docs, click File -> Save as Google Docs and save it as a Google Docs file.
Now, if you open it, the option to insert icons is under the Add-ons -> Insert icons for Docs, and works just fine.
A simple instructional or something like that would be a good idea. @Owner, if you want someone to pull up something, let me know. I do freelance work for small bits and pieces like this.