Almost a year ago Google updated Docs to a new and enhanced version. The only downside was that the new version couldn’t be used with already-existing docs, you had to create new ones. Today, Google is rolling out a built-in system for Docs that will allow you to convert your old documents to the new editor. The feature is still under development so it won’t work perfectly for all documents, but it is worth a try.
When you open a Google Document that was created prior to the new version of editor, you’ll now see a prompt appear at the top that asks “Would you like to see this document in the latest version of the editor?” You can then Click the Preview button and get a live view of how the converted document will look.
If the preview looks good, Click the Update this document link and Google will permanently convert the document to the latest version. Groovy eh?
When you have a lot of documents Docs account, it might be a little tricky to find which ones are using the old editor. Unfortunately, Google has added in any visual indicator for “old" documents, neither is there a listed creation date. The only way to find your old documents, is to open them up manually one at a time; but it only took Google a year to bring out a conversion feature, let’s cut them some slack…
Via [the Google Docs blog]