In previous publications we have demonstrated the use of laser intensity modulation to embed information in halftone and text documents. In those experiments we were able to embed and correctly decode 33 bits in a 12 point page of printed text. In this paper we will present our current work on developing a channel model for a text document. This model will allow us to define capacity bounds for the channel and to better understand the modulation and detection techniques that can be used to reach that capacity.