I have AEM Forms 6.4 on Windows Server. Just now downloaded AEM Forms add-on package for Windows (AEM-Forms-188.8.131.52-WIN-5.1.14.zip) from AEM Forms releases, but how to install it? I cannot see anything "installable" in the zip file.
Yes Content Repository and crx-repository are same. If you intend to use only "Document Security" module, then you do not require aem-forms-add-on package and Content Repository. See the LiveCycle ES4 SP1 > AEM 6.4 Forms on JEE section in the following article for detailed upgrade instructions: