How to "print" a web page to a PDF in Safari on iOS (iPad)?
This is now possible on iOS 10 (and possibly earlier). It works for anything that can be printed


Tap the Share button (in Mail, this is in the Reply button)
Then Print
Now, pinch to zoom the preview (or with 3D touch, pop) to get a full-screen view of the print preview. This is actually a PDF of the view and has its own share pane, so you can, for example, email the PDF.