Overlaying electronic ink over a document. A typical scenario may be where one it would be useful to mark up a document with electronic ink, such as by making handwritten comments, drawings, and the like over the underlying document. In some embodiments, a developer may easily define an inking surface, such as a transparent or opaque window, over a document. The inking surface may act as an input interface such that a user may write onto the inking surface such that is appears that the document itself is being marked up.