How do I download PDF documents from Gmail? When I receive a PDF attachment, the Gmail app only gives the option to preview it, not download. It opens in the default PDF reader (I have Adobe's reader).

How can I save the PDF instead?
Attachment2SD will do the trick.

After you install it when you click on the PDF attachment in the Gmail app it'll pop-up the "Complete Action Using..." dialog.  Choose Attachment2SD and it'll download to a directory on your SD card, where you can immediately open it or save it for later.  This works with all kinds of files, not just PDF.