Updated June 10th, 2019.
It’s very, very handy to be able to make a PDF from whatever document you’re working on. The easy, built-in way to do it involves the Print command.
You’d think that making a PDF would involve Save As… or Export… (and in some cases, it does) but going to File/Print… always works. Always!
In the Print box, look for a little PDF button at bottom left.
Click that button and a menu drops down, and everything you need is right there in the menu. The button is always there, no matter what you’re printing. You can even choose to send the PDF, via Mail, right there in the menu.
Your original document is still there and editable. What you’re doing is making a copy, in PDF form.