12.1 The Preflight button in InDesign, at the lower left corner of the screen. Click on it to show Preflight options.
InDesign has a Preflight option in the lower left corner of the document window which enables you to check various aspects of the document before making a final PDF. A green button means everything governed by the current profile is OK, whereas a red button means the document has a problem (fig. 12.1). However, the default preflight profile will not warn you about the inclusion of RGB images. As this is extremely useful, it is a good idea to create a new profile which will warn you.
To do this, click on the small ...