If I've already filed my taxes and they are downloaded to be mailed, am I still able to get an extension?

You either filed them or are holding on to the paper version waiting to put them in the mail. If you have filed your return, you have to reason to file an extension. If you are still holding on the the paper version, you can. However, if your taxes are complete, you have no reason for an extension. If you owe, you are still expected to pay on time and will receive a penalty.