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, 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 that could lead to the undesired situation.