Huh, well I just tried to download a pdf from gmail and got the same thing. Within the email window there was a button down at the bottom by the attachment icon. It said Preview. I click that and I can indeed preview but there is no save option. If I tap the screen, I get three icons at the top. The first is a folder, which takes me to an Acrobat Reader interface, but there's nothing there. The middle icon, an arrow pointing up, is disabled. And the other is just a search button. If instead I hit the phone's menu button, I get a view mode option, an About Adobe Reader option, and an Open option. You'd think the Open option would open the full file in Reader or something, but nope, it just takes you to the same Reader screen where, at least on my phone since I have no saved PDFs yet, it says "No PDF Files Available".
Long story short, I don't see a way to detach/save either.