There are MANY different points on the document which are anomalous to this sequence of events...
All that I'm saying is that this document is a manipulation of that original... if you seriously want to dispute that I'll go over all the different points and explanation, but it might as well be called a fact.
The REASONS for that could be anything... at the most innocent as a way to guarantee that this file could not be used so that others will try to steal his identity (foolish as that prospect would be on it's own), to a simple distraction from political troubles, OR at it's worst an attempt to politically discredit the GOP (with Trump the closet liberal claiming to run as a republican only to "force Obama" to release that document)
Even to say that this is a result of 'layering' is somewhat of a joke because scanners work in such a way that it's a 'what you see is what you get', and character recognition software is not THAT sophisticated yet, in the sense that it works, but has limitations.
The best part is that the document is still there untouched on the whitehouse website, so when you doubt me, then you can look for yourself.