as the document is created in indesign then i strongly suggest making black pages “black” in the indesign file itself. just like acrobat, it has a similar separations preview. my advice is to go to a black page and toggle the black separation off. if colours other than black appear on the page, then they will need to be made black only. a good example of this may be a picture which appears black and white but is in fact RGB… in this case the picture will need to be opened, converted to greyscale, saved, and update in indesign.
otherwise, acrobat can force pages to greyscale using the advanced/print production/convert colors menu. assuming acrobat 9 is being used, open that menu item and look at the dialog box. in the centre left of the dialog box there will be a checkbox which says “convert colors to output intent”. click on this checkbox and in the dropdown field associated with it, click any one of the seven options at the bottom (dot gain 10% thru to gray gamma 2.2). in the checkboxes beneath this, only click the one which says “preserve black”, and in the dialog below, select the pages that these adjustments should be made to.
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