DOC is also the leading document format for PalmOS applications.
Its chief advantage over the Notebook format is that it allows very big documents (megabytes), and that it can be natively compressed (this is a major concern on a small system like the Palm).
You can produce DOC documents with several filter applications that run on desktop systems. There is also good PalmOS DOC editor called QED.
For reading DOC archives, there is a good but limited GPL program called CSpotRun. Other contenders, not GPL'd, are Aportis Doc and TealDoc.
DOC, in the Italian winery context means Denominazione di Origine Controllata, "controlled origin naming".
To say that, for example, Chianti has received the DOC mark means that there is a painfully detailed spec (called the capitolar) that describes exactly what you can call Chianti: what kinds of grape it can be made from, what part of the country the grapes must come from, what wine-making method is acceptable, how long it should be aged, in what kind of bottle it should be bottled and what should be its chemical properties.
Conversely, the DOC mark on a Chianti bottle states that that particular bottle satisfies the DOC capitolare for Chianti. Misuse of a DOC mark gets people in trouble real fast.
The DOC mark is part of the Italian food laws.