When you choose to save a Google Docs file for editing offline it creates a file in your Google Drive folder. However, that file is just a URL to the online Drive. Do you know where actual file is stored?
The same question was posted on Stack Overflow back in 2012.
In the accepted answer it says
It turns out the offline documents are stored in the HTML5 FileSystem.
I added a number of large images to a document with the Chrome "Offline Docs" enabled and was able to see the FileSystem storage directory grow appropriately.
I then used the HTML5 FileSystem Explorer extension for Chrome to view the file structure of an offline document and was able to confirm that the images were, indeed being retrieved from the HTML5 FileSystem when Chrome was offline.