How to print emails, webpages, and photos as PDFs?

Print to PDF [$3.99 - App Store link] is exactly what you are looking for! It’s a universal application for the iPhone and iPad that adds “Print to PDF” as a printer when using Apple’s built in printing feature. This includes, emails, email attachments, websites, and photos. All you need to do is have Print to PDF running in the background.
Another really cool feature about Print to PDF, is that if you have multiple devices running Print to PDF and they’re all connected to the same WiFi network, you can print to any of those devices.