Using the Safari web browser in iOS 12, you can save a webpage in PDF format. Here’s how:
Open Safari on your iPhone or iPad.
Navigate to a site and then the webpage you want to save as PDF.
Tap on the Share button.
In the Activities sheet, tap on Create PDF.
When the PDF is created tap Done.
Tap on Save File To …
Choose the location to which you wish to save the webpage as a PDF.
(This how-to is based on my experiences and info on Apple's support pages — where the images sometimes come from.)