Per features available through at least Acrobat 8 -
1) ability to adjust baseline of text, or portion of text
2) ability to adjust letter spacing and word spacing - have PDFs where the source must have been justified, and current controls don't have good way to correct this.
2) set fill and stroke for text
3)find/replace single character or character codes - for example, find a 'fi' ligature and replace it with the letters 'fi'.