Acrobat displaying certain fonts as glyphs or wingdings?

I have a user whose Acrobat is displaying certain fonts incorrectly when it initially loads a PDF document she's received. The documents contain a mix of different typefaces but it seems like the problem font is Arial Bold. Text displays as a mix of special characters and symbols. The only way we've found so far to get the text to display correctly is to edit the PDF she received, change the affected text boxes to a different font then change it back to Arial.