Just select “Save as PDF”, give it a name (at the very least), as well as other optional pieces of information such as a subject and any keywords you want to add to make locating the PDF easier later on. Let’s assume, however, that you just want to save your document as a PDF. But there are also others to directly create and mail via the Mail app, or send it via Messages.
There are a few choices you can explore here, the most obvious being “Save as PDF”. You will need to click on this menu to access further options. Now, note the “PDF” controls in the lower-left corner of the Print dialog.