1. A method for annotating a printed document having preexisting content, the method comprising: identifying a first copy of the printed document having preexisting content, wherein the first copy of the printed document is printed from a digital document having a corresponding digital version of the preexisting content; storing first handwritten annotations captured from a first smart pen interacting with the first copy of the printed document having the preexisting content; identifying a second copy of the printed document having the preexisting content, wherein the second copy of the printed document is printed from the digital document having the corresponding digital version of the preexisting content; storing second handwritten annotations captured from a second smart pen interacting with the second copy of the printed document having the preexisting content; merging the first handwritten annotations and the second handwritten annotations to generate a collective set of handwritten annotations; associating the collective set of handwritten annotations with the digital version of the preexisting content; storing the first and second captured handwritten annotations in association with the digital version of the preexisting content as an annotated digital document; detecting a background color of a particular area of the annotated digital document, the particular area having at least a portion of the first captured handwritten annotations; and formatting the portion of the first captured handwritten annotations in the particular area of the annotated digital document to have a color selected based on the detected background color.