Saving document causes unreadable text

Writing a newsletter, I have been saving the draft file for a week with no problems. When I saved it as a final version, most of the pages' text looked like the above page. I am able to rectify by selecting the text, making it bold, and then unbold. I was able to save without this issue reappearing. This causes me alot of work, before I can have a finished product. This issue has happened many times in my experience with Adobe Pro, but not every time I save a file.
