Just wanted to chime in here with @benwiggy that I continue to have the same problems with Affinity on imported PDFs. (In fact, I'm guessing from the same source applications.) I am usually simply trying to rearrange elements on the page, or hide certain elements from being printed. I'm not actually even editing the text, but just opening the file destroys anything that uses a ligature.
Like Ben, I am forced to do this kind of work in Illustrator at present, but I would much rather do it in Publisher, and it doesn't seem to be an unusual request to open a file that has embedded characters correctly, especially when I do have the fonts installed on my computer.