It's probably not forged. The Sheriff presented the layers argument. However, that was shot down almost a year ago. When you use the software tools that were used on that document, you get the kinds of effects the Sheriff meticulously documented. To be sure, they are there, but they don't add up to forgery.
Remember, there is an original on file in Hawaii. If the document Obama gave out were ever shown not to match that original in all material facts asserted, the game would be up. Obama and his lawyers know that. But if they do match, then the only recourse is to impeach the original on file. And, given the passage of time, that's likely not doable either.