iOS has a hidden feature that allows you to generate PDF file from the print preview screen. Yes, PDF export is built into iOS and you do not need to install additional app. Unfortunately this feature is available only on iPhone with 3D Touch.
When viewing a page on Safari or working on a document in Notes app, tap on the Action/Share button and select the system Print function. This will open the print preview page with print options on top half of the screen.
Press on the preview image (3D Touch) to bring out a Quick Look preview of the PDF file. You can then share the PDF, save to Dropbox etc from the Quick Look screen by using the standard iOS share extensions available on your phone.