You may have come across a situation when you print or make a PDF in Adobe InDesign where some of your type appears bolder than the rest of the text – and it’s not because you wanted it that way. Here’s a brief explanation of what’s going on. When you use transparency in your document, either by placing a layered PSD file, using glow or drop shadow effects or setting an object’s transparency to something other than 100% Normal, AND that object is on TOP of your text, the file is “flattened” when you print or export to PDF. Flattening is essentially rasterizing or outlining the text which interact with the transparency area. You can adjust the settings in your preferences, but you cannot avoid the process. This can sometimes make the text appear bolder than text that is not underneath the immediate area of the transparenct object.
To avoid this flattening issue, simply make sure that your text is either on top of any objects using transparency, or on a layer which is higher up in the layer order than the layer containing the transparency.
Along the same lines, you may also notice that sometimes your document looks fine in InDesign, but when you print or export, some objects have a slightly lighter box around them, almost like a bounding box. This can occur when you place an image that is in the RGB color space into your CMYK-based InDesign document. This is especially noticeable if you place a layered PSD file on a CMYK background in InDesign and the image you place either has edges that don’t meet the frame edges in the object container (such as a circular image placed in a square frame). It can also happen if you place a colored image as your background of the entire page in InDesign. You won’t notice it when you export or print unless you set a drop shadow (or some other form of transparency) in your InDesign document on top of the RGB background. The solution is simple. Make sure your Photoshop images are all CMYK.