Limitations: Only the first page of a PDF will be displayed inline. This restriction is according to the specs. And you cannot point to a specific page of a multi-page PDF document like you can with an anchor link (ex. <a href="....pdf#page=2>).
So this technique is good for one-page PDFs or to display the first page of a multi-page PDF as a preview image, linked to the full document. If you use a Markdown editor like Ulysses, know that you can similarly use a PDF as an image.