Or use an application such as Acrobat or pdfToolbox to convert any fonts into curves. I would consider this as a better option. Even with ID or QXP (that can place a PDF using passthrough) I often use this option for ads, etc.
To explain it the other way round:
Most applications display PDFs correctly. Why? Because they display it. The PDF (normally) has everything incorporated, what is needed – especially the used fonts or subsets of them.
Some applications allow editing a PDF. Acrobat Pro does it to a certain degree for example. Now, you sometimes can see, that the PDF, which was displayed correctly formerly, may change the fonts as soon as you try to edit the text.. The reason of this are (a) copyright issues and (b) sometimes the fact, that only a subset of the font was embedded (—> if the glyph „z“ isn‘t embedded, you can‘t use it.). Additionally it would need coding efforts to retrieve the embedded fonts from the PDF to re-use it. But, as I said, that is in most cases not only a technical, but also a legal issue. So: Acrobat Pro only enables us to edit a PDF, when the exact(!) same font, which is used within the PDF, is installed on our computers – and so does Illustrator.
Affinity Publisher isn’t able to simply display a PDF, as, for example InDesign, QuarkXPress, Apple’s Preview or most other applications do. Affinity Publisher tries to import the PDF in a way, that makes it editable. And exactly that is the pitfall: Using a font, embedded within a PDF, normally(!) is only legal, if you own this font, respective, if you have it installed on your machine. Other apps don’t have to struggle with this problem, because they don’t try to (re-) use the embedded fonts.
So, if you open/place a PDF with fonts, which are not installed on your computer, the font will change into a standard font. If Affinity Publisher had a PDF „Pass Through“ mode (see point 1.), this wouldn’t be an issue, but …
