You have two options to save your webpage as a PDF in Safari. Some options produce a slightly different result depending on your webpage. Both options are listed below.
Go to File > Export as PDF.
Click "Save".
An alternative way to save your webpage as a PDF is through Print Settings.
Go to File > Print.
On the bottom left hand corner, choose "Save as PDF" from the PDF Dropdown.
Name your file, and then click "Save".