Preview and Publish show smart symbols differently

[donjohnson24]

If you view my page https://www.donjohnson24.co.uk/Average-Man.php you will see lots of � symbols where 'smart' versions of dashes and inverted commas show that the top part of text was originally cut and pasted from a version of Word where the Options to insert these characters had not been unticked, unlike the second half which was from a Word version that HAD unticked the 'As you type' options. My query is why the � symbols do NOT appear when Preview is selected rather than Publish. Could it be to do with the fact that I'm using a PHP page?

[Pablo]

Your page is configured to use an outdated HTML version.
Please set the document type to HTML5 and character set to UTF-8.

[donjohnson24]

Thanks, Pablo - such prompt and efficient service! The same changes are probably needed on all the old stuff I created originally years ago and have failed to keep updated properly.