Convert fonts to outlines not working

I have this PDF that I have converted the fonts to outlines but when I open it in Illustrator I still get a missing font error. Everything looks to check out in Acrobat. Before I apply convert to outlines, under Document Properties>Fonts, there are fonts listed. And after I apply convert to outlines there are no fonts listed. So I'm not sure why I'm getting this error in Illustrator. Does anyone have any suggestions? Thanks!