Enfocus PitStop Professional is a high-end plug-in for Adobe Acrobat that allows users to manipulate and preflight PDF files in many ways. The big advantage of the Enfocus PitStop method of color conversion is that you have a choice as to how you convert the colors of each individual object in your document. However, if you want to convert colors globally throughout the PDF file, this can be done with equal ease.
Make sure you've installed the latest version of PitStop. Open the PDF file linked above. Now open the PitStop inspector (Window > Show PitStop Inspector...) and click on the image tab. Now chose the PitStop "Select Objects" tool (in you toolbar it looks like and white arrow outlined in purple.
If you're using our sample file, click on the picture of the girls in the top right of the PDF file. If you're using your own image, click on it. The PitStop inspector will show you that the image is in RGB mode as below.
To covert the color mode of this image couldn't be simpler. Make sure the image is still selected then click on the Color tab in the PitStop inspector. Press the CMYK button. This will convert the color of the selected object to CMYK. In the PitStop Inspector, click again on the image tab and you'll see the color mode has been changed to CMYK.
OK, so you want to stamp your document. Maybe you need to give reviewers some advice about the document's status or sensitivity. This tip from author Ted Padova demonstrates how to add stamps with the Stamp Tool along with related comments.