Q. I see that CMOS 8.155 has “Google Docs” as an example. Would you also cap the singular “Google Doc,” or because it’s not the name of a program and just referring to a document in the Google Docs platform, would it be “Google doc,” akin to “Word doc”?
A. The answer depends on how formal you want to be and whom you are writing for and why. Many writers would consider “doc” to be too casual for formal prose. Unlike “app”—which was considered casual a generation ago but is now a universally accepted synonym for “application” or “program”—“doc” is still listed in Merriam-Webster as an abbreviation only.
But if you do write about docs instead of documents, be consistent. Your suggestion that a Google doc is akin to a Word doc is exactly right. If, on the other hand, you work for Google or you’re describing how to use Google Docs, you might write “Doc” with a capital “D”—as in, “Create a new Google Doc.” (That’s what Google does in its tutorials for teachers.)
Otherwise, refer generally to documents created or edited in Google Docs; ditto for Microsoft Word. This advice extends to spreadsheets created or edited in Google Sheets or Microsoft Excel and to slides created or edited in Google Slides or Microsoft PowerPoint.