doc is undefined but should refer to the MS Word file extension (like docx does). However, it is synonomized with documents. It should be unsynonomized (or is that dissynonomized?), the relevant questions retagged from documents to doc, and the tag defined.
document is synonomized under documents, but both are meta tags that can refer to almost any user file that contains readable contents. They can probably be simply deleted. If tagging questions to differentiate reference to the user file from of, say, software installation/configuration is useful, application-specific tags should be created.