Bumped! Are you listening Affinity?
This is a really important feature that Affinity should absolutely implement, if it hasn't already (I only have V1) – the ability to choose to open a PDF with the text converted to outlines. I've been using the Mac professionally since 1995 and the program that could always do that in the past was Deneba, now ADC, Canvas. I waited 15 years for Adobe Illustrator to do this and they finally implemented it recently. Now I'm trying to move to Affinity for everything, but this is a bump in that road.
Now in Illustrator, trying to open a PDF with fonts that aren't installed (as none of them ever seem to be) brings "The document contains PDF object that have been reinterpreted: To preserve appearance, some text has been outlined." This isn't as nearly as good as ADC's Canvas, which gives you the option of substituting fonts or converting them to outlines. But Designer, at least V1, will only substitute fonts, which usually always badly mangles the PDF.