Cannot generate a front cover on the first page of the e-book viewer

[Heathside Boy]

I had been given the advice on how to generate a front cover (first page) inside the E-book viewer before. I tried it again recently I cannot seem to do it this time.

This is what I did.

First of all, I imported a PDF version of a book from my computer into Calibre from the "Add Books" tab. Then I converted it to e-pub format.
I kept and followed the advice that I was given before on how to generate a front cover inside the E-book viewer. That was as below.

Preferences » Conversion » Common Options » Structure Detection » Insert metadata as page at start of book

Covers (metadata) only update if you convert (EPUB to EPUB).

I think calibre also stores individual conversion settings per book. If you've already converted it once, it's probably not using the new settings. On the conversion dialogue, clicking on the "Restore Defaults" button would probably do the trick.-

Preferences > Common Options > Restore defaults > Apply

After trying all that, it still did not work as it did before when I first got those instructions for another book where it worked.

Am I missing anything or doing anything wrong?

Any other ideas on why it may not be working and what I should be doing to make it work would be truly grateful.

Thanks

HB