Despite numerous predictions of the paperless office, knowledge work is still characterized by the combined use of paper and digital documents. Digital pen-and-paper user interfaces bridge the gap between both worlds by electronically capturing the interactions of a user with a pen on real paper. The contribution of this paper is two-fold: First, we introduce an interaction framework for pen-and-paper user interfaces consisting of six core interactions. This helps both in analyzing existing

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... practices and interfaces and in guiding the design of interfaces which offer complex functionality and nevertheless remain simple to use. Second, we apply this framework and contribute three novel pen-and-paper interaction strategies for creating hyperlinks between printed and digital documents and for tagging both types of documents.