10. A computer program product for annotating a printed document having preexisting content, the computer program product comprising a non-transitory computer-readable storage medium containing computer program code for: identifying a first copy of the printed document having the 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; receiving from a first smart pen, first handwritten annotations on the printed document, the first handwritten annotation captured using the first smart pen; 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; receiving from a second smart pen, second handwritten annotations on the second copy of the printed document, the second handwritten annotation captured using the second smart pen; 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.
10. A computer program product for annotating a printed document having preexisting content, the computer program product comprising a non-transitory computer-readable storage medium containing computer program code for: identifying a first copy of the printed document having the 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; receiving from a first smart pen, first handwritten annotations on the printed document, the first handwritten annotation captured using the first smart pen; 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; receiving from a second smart pen, second handwritten annotations on the second copy of the printed document, the second handwritten annotation captured using the second smart pen; 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. 14. The computer program product of claim 10 , wherein the non-transitory computer-readable storage medium further contains computer program code for: performing character recognition on the digital document to recognize characters in the preexisting content and storing recognized characters in the annotated digital document.