Why are fonts being printed incorrectly from a PDF generated in LibreOffice?

I’ve been printing a book using LibreOffice since 2011. Two proofs ago, some of the fonts printed incorrectly from the PDF, and I realized that aspects of the formatting were inconsistent, and corrected this. In the most recent proof, the first errors have disappeared. But now all the italics in the text are printing in a medium version of the text font, and not in italics. Should I create a specific style for italics? Any help with how to solve this issue would be greatly appreciated!

What version of LibreOffice are you using now?
Previous version of LibreOffice which worked properly?
Operating system?
Font family being used?

Check your fonts - it looks like some are missing. You can see which fonts are installed on the PC by Start > Control Panel > Fonts or by clicking C:\Windows\Fonts.

The font showing in the Writer font drop down selection box is the font the document is asking for - it is NOT necessarily the font being used to create the display or print the document. This is because, if the font being asked for is not installed on the PC, Windows (or other operating system) will silently substitute a different font which is available.

The TestFonts add-on is invaluable for finding missing fonts which the document is asking for, but which are not installed on the PC.

Also you can embed the font in the PDF with the Export > PDF options dialogue.