I'm writing an extension that would ideally read files after they are downloaded (through the normal download process). Is that possible? I can get the filename through chrome.downloads operations, but I can't find ways of reading the actual bytes. I don't need to write or move them, just read.
I struggled with the exact same problem and finally found an easy workaround to read the content of downloaded files from a Chrome extension.
You just need to add a permission to file://*in your manifest file and once you have your file's path in the system (with chrome.downloads.search in the filename property), make a GET XMLHttpRequest to the url file://{filepath}.