We present PaperProof, a paper-digital proof-editing application that allows users to edit digital documents by means of gesture-based mark-up of their printed versions. This enables users to switch seamlessly back and forth between paper and digital instances of a document throughout the document lifecycle, working with whichever medium is preferred for a given task. Importantly, by maintaining a logical mapping between the printed and digital instances, editing operations on paper can later be integrated into the digital document even if other users have edited the digital version in parallel. The system is based on Anoto digital pen and paper technology and is implemented using the iPaper framework for interactive paper.