A method for determining document compatibility between documents stored locally on a plurality of user devices, while maintaining the confidentiality of each of the respective documents. The method includes requesting and receiving a token from each of the plurality of user devices, the token indicative of the presence or absence of a specific element in each respective document. The method further includes comparing the value of each of the respective tokens. When each of the tokens have a true value, the specific element for each respective document is determined to be compatible and sends a message to each of the plurality of user devices indicating the compatibility of the respective documents. When at least one of the tokens has a false value, the specific element for each respective document is determined to be incompatible and sends a message to each of the plurality of user devices indicating the incompatibility of the respective documents.