It sounds as though your text may be getting rasterized upon export to PDF. Are you using a PDF Export preset? What is the intent (print, on-screen), and what are your export settings?
I previously wasn't using an adobe preset, however I just created a pdf file with the adobe preset "small file size". I haven't changed any of the settings, but it perhaps could be better. My project is a portfolio, so the intent is on-screen and sendable via email. I've had this printed as well, will no issues.
What is the best way to deliver the best quality with a small file size? I just would like the text to be easier on the eyes to read.
...before I go ahead and change the text of a 30+ page document ...
As a side note to this discussion, if you make it a firm practice to use Paragraph Styles and Character Styles for all of your text formatting, it would not matter if it was a 200+ page book, the formatting changes could be done in moments by adjusting the styles. (of course, you would still have to check for awkward reflow or overset).