Abstract: The Hill cipher algorithm only encrypts messages in the form of document and can only decrypts the same message provided the matrix used as key is non-singular. In this paper, we propose an algorithm for decryption of documents to be possible for both singular and non -singular matrices as invo- lutary key alongside giving practical examples by using two by two and three by three involutary keys for singular and non singular matrices to illustrate our result when encrypting and decrypting documents.