Visually rich documents (VRD) are physical/digital documents that utilize visual cues to augment their semantics. The information contained in these documents are often incomplete. Existing works that enable automated querying on VRDs do not take this aspect into account. Consequently, they support a limited set of queries. In this paper, we describe Juno -- a multimodal framework that identifies a set of tuples from a relational database to augment an incomplete VRD with supplementary information. Our main contribution in this is an end-to-end-trainable neural network with bi-directional attention that executes this cross-modal entity matching task without any prior knowledge about the document type or the underlying database-schema. Exhaustive experiments on two heteroegeneous datasets show that Juno outperforms state-of-the-art baselines by more than 6% in F1-score, while reducing the amount of human-effort in its workflow by more than 80%. To the best of our knowledge, ours is the first work that investigates the incompleteness of VRDs and proposes a robust framework to address it in a seamless way.