what version of Acrobat do you have?
Acrobat 9 Pro - Advanced > Preflight > PDF Fixups > Convert to Gray. Tested, works here.
Guess I should have been more specific in that it is a 4-color job, it's just the particular table (Placed PDF) with lots of black text is not 100% K it's CMYK, some of the table cells are colored and the text is 8 pt.
I ended up making a couple of phone calls & got the original Word file and placed it in ID and spent a good hour or so re-formatting, text is all black now.
– Although – I didn't know about the Fixup thing in Acro, I could have used that many times before...
FWIW, the correct(?) best tool would be Enfocus Pitstop, and if you find yourself frequently in this situation, its cost would be justified.