Adobe using "Z@RA0F7.tmp" font when trying to edit PDFs

I've been working on this PDF for the past two days, and all of a sudden Adobe is changing the font to a "Z@RA0F7.tmp" font when I try to go back and edit what I've already typed (see screenshot below... the highlighted text is supposed to say "of the"). I've tried changing the font, but as soon as I start typing Adobe changes it back. I've tried highlighting the text and then changing it... it will change it to anything bu Arial, which is the font that I happen to be using. Now, if I completely delete the entire text box I can change the font, but I've already got a lot of content and do NOT want to start over. Any solutions????