Thanks, all. Andrew: have you noticed that on other sites?The original observation of the problem was with Edge on Windows 10.That was followed by "I've tried internet explorer and all I get is a box with a cross through it ( more than edge shows!), so we tried a mobile phone and get a small box that we cannot open up to show the pdf's."There's one reference to it in the archives: "That's because it's not an image - it's a PDF, and most browsers don't support embedded PDFs using <img> tags."
And the code in the page discussed in this thread is probably:
<p><img alt="" src="/sites/default/files/inline/images/Xflow%20cooling.pdf"></p>Jonathan