You keep opening PDF documents all through the day using Adobe Reader. But, somewhere during that time you notice that the text in certain PDF documents has started to be rendered in jagged or aliased fonts.
Adobe Reader changes its text rendering setting by itself on certain kinds of PDF documents. To set it back to render text smoothly with anti-aliasing: Go to Edit → Preferences and drill down to Page Display → Rendering → Smooth Text. The setting for this would be None. Change it to For Laptops/LCD screens.
Tried with: Adobe Reader 9.3.3