1. A method of embedding into a text document generated by a licensed software License Identification Signature of the software wherein each original copy of the software has been assigned a unique Software License Code (SLC) and a unique License Identification Key (LIK) by a Licensing Authority, the method comprising: computing a Document Hash Value (DHV) of the text document, obtaining from the DHV a License Identification Code (LIC) of the text document by using the LIK, and embedding invisibly into the text document the License Identification Signature (LIS) formed by the SLC, DHV and LIC after the LIS has been encoded by using character attributes.