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For print shops to win bids in a competitive market, it is important to price jobs correctly. It is also important that print jobs have predictable costs to make a profit.
Printers often receive jobs which appear to contain a mix of colour and B&W pages and the job is priced accordingly to win the bid.
Sometimes these mixed jobs generate all colour click charges and all the profit on the job is lost or creates a financial loss. I’ve had customers who have run very large mixed jobs only to find out every page was a colour click even though most of pages appeared to be black and white when they opened the job in Acrobat.
To avoid this problem you can preflight the job in Acrobat Pro to find out which pages are colour or B&W and then convert the pages that should be B&W. Versions 8 and 9 of Acrobat Pro have excellent tools for print production to check for many things that are important to a print shop.

Preflighting in Acrobat Pro

If you check under the Advanced or Print Production menu in Acrobat Pro 9 you will see Preflight. Preflight is also available in Acrobat Pro 8 and it is similar to 9.
You can download this sample file to try preflighting in Acrobat Pro. The sample PDF file has one page with colour elements and a second page which appears to be B&W. Both pages will generate colour click charges on a digital press. The sample was created using MS-Word and Excel and converted to B&W using the high quality print setting.
When you open Preflight, it loads a large variety of preflight profiles to check for various standards compliance and issues you might encounter when printing. We are going to use the Digital Printing (B/W) profile located in Digital printing and online publishing section. If you click on the edit button you can see all checks that are done by this profile. Some of the checks will generate warnings while other checks generate errors or information.
Click on analyze to preflight the PDF file.
Once it is done preflighting, a preflight report is created under the Results tab. Click on the drop down beside Document Images on CMY plates. You will see one colour image on page 1 but there are many colour images on page 2. Page 2 appears to be a B&W page when you look at it or print it!
Click on any of the colour images and then click on the show button. This will highlight the colour element in the PDF file. If you click on Show in Snap the colour element will be displayed in a small window.
There is another way to check pages for colour elements. Close the Preflight window and select Output Preview under the Print Production menu.
Output Preview show separations by default and will list all colour plates. If there are Pantone plates in the job it will list the Pantone colours as well. Deselect the check box beside Process Black. If there are no colour elements on the page, all the black items should disappear. In the sample PDF file nothing disappears! We can fix this problem.

Converting Colour Pages to B&W

You can convert the colour pages to B&W by selecting Convert Colours under the Print Production menu. In this example we need to convert page 2 but you can convert both pages to see what happens.
In the Convert Colour dialog box make sure Any Object, Any Profile, Convert to Profile is selected. Beside Conversion Profile, click on the drop down menu and scroll to the very bottom where you will see several profiles for converting to B&W. Select Gray Gamma 2.2. This is B&W on a PC. The various Dot Gain profiles also convert to B&W and they will make images lighter or darker depending on which one you choose.
At the bottom, under convert pages, you can select which pages you want to convert. Try converting all the pages so you see the colour image on page 1 change to grayscale. After you have converted the colours, use save as to create a new version of the PDF file.
Now try preflight again with the Digital Print (B/W) profiles and you will see all the colour objects are gone.

Summary

To save yourself money, time and frustration, you should always preflight any file you receive from a customer. The preflight tools in Acrobat Pro 8 and 9 make it easy to correct many printing issues.