How was the PDF created in the first place? Did you create it yourself?
Is this on a Mac?
Yes it's on a Macbook Pro and I downloaded a template in the form of a PDF from a website and opened/edited it on Acrobat.
In that case you might be running into a problem that has nothing to do with Acrobat or Reader, but is something Apple has to fix (I reported it more than a year ago): More Missing Characters - KHKonsulting LLC