Document Logic is a simple yet powerful framework to infer risks in business processes. We focus on flows of documents and build a set of inference rules based on document authenticity and a simple trust model. We have built a prototype of a system that checks document authenticity in Maude. Maude is an implementation of rewriting logic. Rewriting logic is expressive and general enough to define other specialized logics, like Document Logic. In our framework, a business process is modeled as a transition system. Our prototype takes a business process and an undesired situation as its input and outputs all the possible risks in the business process.