In a previous post, I described how to convert a color PDF to grayscale in Acrobat 8 Professional. The method I described in converts RGB and CMYK objects properly. But objects made up of 0% C, 0% M, 0% Y and 100% K convert to a value less than 100% black, depending on your color settings.
The good news is, this appears to be fixed in Acrobat 9 Pro. Here's how to convert a color PDF file to grayscale in Acrobat 9 Pro.
1. Open a color PDF file in Acrobat 9 Pro. The file may contain a mix of CMYK, RGB or spot color objects.
2. Choose Advanced > Print Production > Preflight.
3. Select the Convert to Grayscale PDF Fixup, and then click the Analyze and Fix button.
4. Give the file a name and location, and click the Save button. The entire PDF file will be converted to grayscale.