What is POD? What is a POD PDF?
I know, all those acronyms, right? (Tip: you can hover over or click acronyms that you see with a pale line beneath them, anywhere on our website. Like this one: TOOLTIP. That will instantly pop-up a small tooltip, telling you the meaning or definition of an acronym.) In today's world, instead of printing thousands of copies of your self-published book, keeping them someplace, having to ship them, etc., you can use "Print on Demand," or POD, which means that companies like Amazon's Createspace will print and ship an ordered book, at the time that it's ordered. This is called "just-in-time fulfillment," and doesn't mean anything fancier than, the book is made when it's ordered, not before.
Some companies will allow you to upload a Word file, for creation of a POD. This can have unexpected results. Using a PDF as your upload file instead ensures that you don't have unpleasant surprises when you receive your ARC, or "Advance Review Copy." The good thing about PDFs, when used for this purpose is that unlike word-processing files (Word, Wordperfect, Pages, etc.), the appearance of the page doesn't change, depending on what computer it's on, what size screen, etc. PDFs are always the same, and give you nice consistent results when used for POD printing.