Sorry, I don’t buy the argument that the forger didn’t think about the layers when they prepared it to show the public and sent the document PDF unaware that it would be posted as is. ANYONE who has working knowledge of any of the Photoshop products knows that a working copy (PSD file, usually) is very large, mine sometimes are 100mg or more in size. It is very easy to flatten the image to reduce the size in mgs, convert it to PDF or jpeg, and the smaller size much easier to send via email or to post to the web.
Whoever did this, left the document as a PSD file (or whatever PI uses) on purpose.
That’s my 2-cents.
The flattening stuff is a red herring. When you build a document in a program like InDesign or QuarkXpress and then convert it to a PDF, you wouldn’t necessarily be aware that the PDF will contain layers. Also, there are ways to convert such files that don’t result in huge files sizes like you mentioned, but they would still contain the different layers. The telltale problem is the security background. As a layer, it goes away completely and that just doesn’t happen with scanned documents. Second, there’s some kind of layer/clipping mask around the perimeter of the security background, that when the layer is hidden, makes the background larger. Again, this just does not happen with scanned documents.